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Biomedical subjects

J R Roche

Publications and source records attributed to J R Roche.

At least 19 recordsLinked to original sources
PubMed2007

Associations among body condition score, body weight, and reproductive performance in seasonal-calving dairy cattle.

The objective of the present study was to identify and quantify relationships between body condition score (BCS) and body weight (BW) in dairy cows with reproduction variables in pasture-based, seasonal-calving dairy herds. Over 2,500 lactation records from 897 spring-calving Holstein-Friesian dairy cows were used in the analyses. Eleven BCS- and 11 BW-related variables were generated, including observations at calving, nadir, planned start of mating (PSM), and first service, as well as days to nadir and the amount and rate of change between periods. The binary reproductive variables were cycling by PSM, mated in the first 21 d from PSM, pregnant to first service, and pregnant in the first 21, 42, and 84 d of the seasonal mating period. Generalized estimating equations were used to identify BCS and BW variables that significantly affected the probability of a successful reproductive outcome. After adjusting for the fixed effect of year of calving, parity (for cycling by PSM only), and the interval from calving to either first service or PSM, reproductive performance was found to be significantly affected by BW or BCS at key points, and by BCS and BW change during lactation. All reproductive response measures were negatively affected when BCS and BW measures indicated an increased severity and duration of the postpartum negative energy balance. In particular, cycling by PSM was positively associated with calving BCS, whereas pregnancy at 21, 42, and 84 d post-PSM were positively associated with nadir BCS and BW gain post-PSM, and negatively associated with BCS loss between calving and nadir. The results highlight the important role that BCS and BW loss has on reproductive performance, especially in seasonal-calving dairy systems because of the short period between calving and PSM.

Animals↗
PubMed2006

Pre-conception energy balance and secondary sex ratio--partial support for the Trivers-Willard hypothesis in dairy cows.

According to the Trivers-Willard hypothesis, maternal condition at or around conception affects the secondary sex ratio in mammals. However, there are little or no data available on indicators of maternal condition in dairy cows on the sex of the resultant offspring. A total of 76,607 body condition score (BCS; scale of 1 to 5) records and 76,611 body weight (BW) records from 3,209 lactations across 1,172 cows were extracted from a research database collated from one research herd between 1986 and 2004, inclusive. Exclusion of multiple births and cows with no information before calving (e.g., nulliparous animals) resulted in 2,029 records with BCS and BW observations from the previous calving, and 2,002 and 1,872 lactations with BCS and BW observations at conception and midgestation, respectively. Change in BCS and BW between calving and conception and between conception and midgestation was calculated per lactation. Generalized estimating equations were used to model the logit of the probability of a male calf, in which cow was included as a repeated effect with a first-order autoregressive correlation structure assumed among records within cow. Of the BCS variables investigated, there was a linear relationship between the logit of the probability of a male calf and BCS change between calving and conception, the rate of BCS change over this period (BCS divided by days in milk), and BCS at the calving event immediately before conception. The birth of a bull calf was 1.85 times more likely in cows that lost no BCS from calving to conception compared with cows that lost one BCS unit from calving to conception. This increase in odds was equivalent to a 14% unit increase in the probability of a male calf (from 54 to 68%). The amount of BW lost between calving and conception and the rate of loss affected the sex of the resultant offspring. Less BW loss or greater BW gain between calving and conception was associated with greater likelihood of a male calf. Results suggested a positive effect of pre-conception BCS and BW change on secondary sex ratio, agreeing with the Trivers-Willard hypothesis that females in good physiological condition are more likely to produce male offspring.

Animal Feed↗
PubMed2006

Periparturient climatic, animal, and management factors influencing the incidence of milk Fever in grazing systems.

The objective of the present study was to quantify the climatic, animal, and management factors influencing incidence of milk fever (MF) in cows exposed to grazing systems. Data were extracted on 4,469 calvings of multiparous cows in a seasonal calving research herd between 1970 and 2000. Climatic data during the calving period also were extracted for these years. Poisson regression was used to investigate the effect of climate on frequency of MF within year; the offset variable was the number of cows at risk for MF at that time. Generalized estimating equations, with cow included as a repeated effect, were used to quantify the effect of parturition-associated cow and management factors on the logit of the probability of MF. Both univariate and multivariate analyses were performed. Explanatory variables investigated included time of calving relative to the herd-year calving period, parity, body weight, breed of cow, body condition score at calving, weight and gender of the calf, incidence of twin calves, calving inductions, and calving assistance. Odds of recurring MF within cow, as well as the timing of MF relative to day of calving, was quantified using generalized estimating equations with cow included as a repeated effect. Results show significant effects of evaporation, minimum grass temperature, difference between ambient maximum and minimum temperature, and rainfall on the odds of MF occurring, with a greater incidence at greater evaporation, larger diurnal variation in air temperature, greater rainfall, and lesser grass minimum temperature. Cow factors, such as age, excessive or poor body condition score, and requirement for calving assistance increased the odds of MF; a lesser odds ratio was observed in cows hormonally induced to calve and those that had twin births. Results indicate that herd managers may identify the day of greatest risk for MF and cows that are at greatest risk of MF based on climatic, cow, and management factors.

Animals↗
PubMed2006

Short communication: genetic selection for milk production increases plasma ghrelin in dairy cows.

Ghrelin is an endogenous ligand of the growth hormone secretagogue receptor and a potent orexigenic agent in human and rodent studies, but there is limited information about its effect in dairy cows. Twelve low genetic merit and 9 high genetic merit Holstein-Friesian dairy cows in peak lactation that were offered unrestricted access to fresh pasture were used to determine whether genetic selection for milk production resulted in an associated increase in plasma ghrelin concentration in grazing dairy cows. Blood samples were taken prior to the a.m. milking (i.e., baseline) and following 2 h of grazing after the a.m. milking on 2 consecutive wk during peak lactation. Milk production and dry matter intake were greater in high genetic merit cows compared with low genetic merit cows. Plasma ghrelin and growth hormone concentrations were elevated in high genetic merit cows pre- and postgrazing, and there was no significant interaction between genetic merit and time of sampling. Genetic merit did not affect the plasma nonesterified fatty acid or glucose concentration, but the plasma concentrations of metabolites and hormones measured were diminished 2 h after feeding. Data indicate an increase in plasma ghrelin associated with genetic selection for milk production, and an associated increase in dry matter intake.

Animal Feed↗
PubMed2006

Holstein-Friesian strain and feed effects on milk production, body weight, and body condition score profiles in grazing dairy cows.

Data from 113 lactations across 76 cows between the years 2002 to 2004 were used to determine the effect of strain of Holstein-Friesian (HF) dairy cow and concentrate supplementation on milk production, body weight (BW), and body condition score (BCS; 1 to 5 scale) lactation profiles. New Zealand (NZ) and North American (NA) HF cows were randomly allocated to 1 of 3 levels of concentrate supplementation [0, 3, or 6 kg of dry matter (DM)/cow per d] on a basal pasture diet. The Wilmink exponential model was fitted within lactation (Y(DIM) = a + b e(-0.05 x DIM) + c x DIM). The median variation explained by the function for milk yield was 86%, between 62 and 69% for milk composition, and 80 and 70% for BW and BCS, respectively. North American cows and cows supplemented with concentrates had greater peak and 270-d milk yield. Concentrate supplementation tended to accelerate the rate of incline to peak milk yield, but persistency of lactation was not affected by either strain of HF or concentrate supplementation. No significant strain by diet interaction was found for parameters reported. New Zealand cows reached nadir BCS 14 d earlier and lost less BW (22 kg) postcalving than NA cows. Concentrate supplementation reduced the postpartum interval to nadir BW and BCS, and incrementally increased nadir BCS. New Zealand cows gained significantly more BCS (i.e., 0.9 x 10(-3) units/d more) postnadir than NA cows, and the rate of BCS replenishment increased linearly with concentrate supplementation from 0.5 x 10(-3) at 0 kg of DM/d to 0.8 x 10(-3) and 1.6 x 10(-3) units/d at 3 and 6 kg of DM/d concentrates, respectively. Although there was no significant strain by diet interaction for parameters reported, there was a tendency for a strain by diet interaction in 270-d BCS, suggesting that the effect of concentrate supplementation on BCS gain was, at least partly, strain dependent.

Animals↗
PubMed2006

Climatic factors and secondary sex ratio in dairy cows.

The hypothesis for this study was that the prevailing climate around the time of conception was associated with changes in the secondary sex ratio (SSR) in grazing, seasonally bred dairy cattle. Calving date, parity, cow breed, and calf sex were obtained for 8,621 lactations (with single births only) from 1,897 cows between 1970 and 2003 (inclusive). Conception date was estimated by subtracting a gestation length of 282 d from the date at calving. Climatic factors, including maximum and minimum ambient temperature, relative humidity, rainfall, sunlight hours, and evaporation rate, were averaged across the week immediately prior to conception for all lactations. Sun radiation data were available after 1976. Generalized estimating equations, with cow included as a repeated effect, were used to determine the effect of climate around the time of conception on the logit of the probability of a male calf. Breed of cow, year of conception, and parity at conception did not affect the SSR. The odds of a male calf being born were 3.74 times greater when the immediately previous calf born was male. A male calf was more likely to be born following periods of elevated air temperature, greater evaporation, or both. A 1 degrees C increase in average maximum air temperature from the average (18.3 degrees C), during the week immediately prior to conception, was associated with a 1-percentage unit increase in the probability of a male calf being born (i.e., from 52 to 53%). A corresponding 1 degrees C increase in average minimum air temperature was reflected in a 0.5-percentage unit increase in the probability of a male calf being born. The probability of a male calf being born increased by 2.9 percentage units with each additional millimeter of evaporation per day. Results indicate that climatic factors associated with elevated temperatures and greater evaporation may influence the SSR in dairy cattle.

Analysis of Variance↗
PubMed2005

Manipulating the dietary cation-anion difference via drenching to early-lactation dairy cows grazing pasture.

Diets offered to grazing dairy cows can vary considerably in their dietary cation-anion difference (DCAD) and are often well in excess of what has been considered optimal. The effects of a range of DCAD on the health and production of pasture-based dairy cows in early lactation was examined in a randomized block design. Four groups of 8 cows were offered a generous allowance of pasture (45 +/- 6 kg/d of dry matter (DM) per cow) for 35 d and achieved mean pasture intakes of approximately 17 kg/d of DM per cow. Cows were drenched twice daily with varying combinations of mineral compounds to alter the DCAD. Dietary cation-anion difference ranged from +23 to +88 mEq/100 g of DM. A linear increase in blood pH and HCO(3)(-) concentration and blood base excess, and a curvilinear increase in the pH of urine with increasing DCAD indicated a nonrespiratory effect of DCAD on metabolic acid-base balance. Plasma concentrations of Mg, K, and Cl declined as DCAD increased, whereas Na concentration increased. Urinary excretion of Ca decreased linearly as DCAD increased, although the data suggest that the decline may be curvilinear. These results in conjunction with the increased concentrations of ionized Ca suggest that intestinal absorption of Ca or bone resorption, or both, increased as DCAD declined. Dry matter intake, as measured using indigestible markers, was not significantly affected by DCAD. However, the linear increase in the yield of linolenic acid, vaccenic acid, and cis-9, trans-11 conjugated linoleic acid in milk, as DCAD increased is consistent with a positive effect of DCAD on DM intake. Increasing DCAD did not significantly affect milk yield or milk protein, but the concentration and yield of milk fat linearly increased with increasing DCAD. The increased milk fat yield was predominantly a result of increased de novo synthesis in the mammary epithelial cells, although an increase in the yield of preformed fatty acids also occurred. Milk production results suggest that DCAD for optimal production on pasture diets may be higher than the +20 mEq/100 g of DM previously identified for total mixed rations.

Acid-Base Equilibrium↗
PubMed2005

Influence of precalving feed allowance on periparturient metabolic and hormonal responses and milk production in grazing dairy cows.

Fifty-two multiparous dairy cows were allocated to 4 treatments consuming 5.4, 8.2, 10.0, or 11.0 kg/d of pasture dry matter per cow for 27 +/- 9.6 d precalving. This equated to 1.3, 1.9, 2.4, and 2.6% of body weight (BW; not including the conceptus weight). Following calving, all cows were fed ad libitum on pasture. Blood was sampled 17 d precalving, on day of calving, and on d 1, 2, 3, 4, 7, 14, 28, and 35 postcalving. Results suggest that the near-term grazing dairy cow requires 1.05 MJ of ME/kg of BW(0.75) and that previous estimates of energy requirements were underestimated. Precalving plasma concentrations of glucose, insulin-like growth factor-1, and leptin increased quadratically with increasing pasture intake. This was associated with precalving plasma concentrations of growth hormone that declined linearly, and concentrations of nonesterified fatty acids and beta-hydroxybutyrate that declined quadratically with increasing dry matter intake (DMI). Postcalving plasma concentrations of these metabolites showed no lasting effect of precalving feeding. The effect of precalving nutrition on milk production was small, and other than milk fat, was confined to wk 1 postcalving. Milk fat yield increased with increasing precalving DMI and calving body condition score until wk 3 post-calving, after which treatment effects were not evident. These results indicate that the level of feeding in grazing dairy cows during the last month before calving has only small effects on cow metabolic and hormonal status, and on milk production in the first 5 wk of lactation.

3-Hydroxybutyric Acid↗
PubMed2005

Effect of feeding level pre- and post-puberty and body weight at first calving on growth, milk production, and fertility in grazing dairy cows.

The effect of feeding to achieve differential growth rates in Holstein-Friesian (HF; n = 259) and Jersey (n = 430) heifers on time to puberty and first lactation milk production was investigated in a 3 x 2 factorial design. Holstein-Friesian and Jersey calves were reared to achieve a BW of 100 and 80 kg, respectively, at 100 d. At target weight, all calves were randomly allocated to one of 3 feeding treatments to achieve different growth rates. Holstein-Friesian and Jersey calves were fed fresh pasture to achieve average daily growth rates of 0.77, 0.53, or 0.37 kg of BW/d (HF) and 0.61, 0.48, or 0.30 kg of BW/d (Jersey), respectively. Period 1 (prepubertal) was imposed until HF and Jersey treatment groups averaged 200 and 165 kg of BW, respectively. Following period 1, HF and Jersey calves from each treatment group were randomly allocated to one of 2 feeding treatments to achieve average daily growth rates of 0.69 or 0.49 kg of BW/d (HF) and 0.58 and 0.43 kg of BW/d (Jersey), respectively. Period 2 (postpubertal) was imposed until 22 mo, when heifers were returned to their farms of origin. Body weight, body condition score, height, heart girth circumference (HGC), milk production, and fertility-related data were collected until the end of the third lactation. Time to reach puberty was negatively associated with level of feeding, and heifers attained puberty at the same BW (251 +/- 25.4 and 180 +/- 24.0 kg for HF and Jersey heifers, respectively). Heifers on high feed allowances during periods 1 and 2 were heavier, taller, and had greater HGC than their slower grown counterparts until 39 mo of age when height and HGC measurements stopped. Body weight differences remained until 51 mo, when measurements ceased. High feed allowance during period 1 (prepubertal) did not affect milk production during the first 2 lactations, but did reduce milk production in lactation 3. It is possible that the expected negative effect of accelerated pre-pubertal growth was masked by greater calving BW, as BW-corrected milk yield declined in both breeds with increasing prepubertal feed allowance. Growth rate during period 2 was positively correlated with first lactation milk production. Milk yield increased 7% in first lactation heifers on the high feed allowance, which resulted in higher growth rate during period 2. Milk production during subsequent lactations was not affected. Results suggest that accelerated prepubertal growth may reduce mammary development in grazing dairy cows, but this does not affect milk production in early lactations because of superior size. Body weight at calving and postpubertal growth rate management are important in first lactation milk production, but do not affect milk production in subsequent lactations.

Animals↗
PubMed2004

Relationships among international body condition scoring systems.

Scoring body condition and assessing changes in the body condition of dairy cattle have become strategic tools in both farm management and research. Consequently, body condition score (BCS) is being researched extensively throughout the world. However, international sharing, comparing, and use of data generated are limited because different BCS systems exist. In the United States and Ireland a 5-point BCS system is used for dairy cows, whereas Australia and New Zealand use 8- and 10-point scales, respectively. The New Zealand 10-point scale was compared with the scoring systems in the United States, Ireland, and Australia by trained assessors. Cows were assessed visually in the United States and Australia, and in Ireland, cows were assessed by palpating key areas of the cow's body (n = 154, 110, and 120, respectively). Data were analyzed by regression. Significant positive linear relationships were found between the New Zealand 10-point scale and the other scoring systems: US 5-point scale, r(2) = 0.54; Irish 5-point scale, r(2) = 0.72; and Australian 8-point scale, r(2) = 0.61. Those relationships must be interpreted cautiously because respective BCS within a given country were by just one experienced evaluator in each country in comparison to a separate evaluator scoring all cows in all counties using the New Zealand 10-point scale. Also, few very thin or very fat cows limit evaluation across extremes of BCS. However, differences between systems were not accurately predicted by simple mathematical calculations. The relationship may be closer for New Zealand and Ireland (r(2) = 0.72) because both of those scoring systems include palpation of individual body parts, whereas visual evaluation is done in Australia and the United States. The current study is the first to examine relationships among differing BCS systems. These results may be useful for comparing/extrapolating research findings from different countries.

Adipose Tissue↗
PubMed2003

Effect of pregnancy on milk production and bodyweight from identical twin study.

The energy requirements of the fetus through pregnancy have been previously investigated in several slaughter experiments, and many studies have attempted to estimate the effect of pregnancy on milk production. Data from 154 pasture-based dairy cows (77 twin pairs) were subjected to a retrospective analysis to determine the effect of pregnancy on milk production and body weight. A decline in milk yield from 126 d of pregnancy was observed in twins that were pregnant, but the decline was small and insignificant until 147 d of gestation (at 33 wk of lactation), after which pregnant cows produced less milk (0.8 kg/cow per day). Protein and fat concentration increased in pregnant cows from 77 and 133 d of gestation, respectively. The yield of milk fat and protein was not affected by pregnancy until 168 d of gestation, after which pregnant cows produced less milk fat (0.06 kg/cow per day) and milk protein (0.04 kg/cow per day) compared with their nonpregnant twins. Body weight was higher in pregnant twin cows after 90 d of gestation and continued to increase until the end of lactation (182 d of pregnancy). Fitted splines showed higher milk protein concentrations in pregnant cows throughout lactation, and milk protein yield was higher (20 g/cow per day) during the breeding season (between 12 to 17 wk of lactation) in pregnant twins. Higher milk yield and energy secreted in milk (net energy for lactation) were also found in the pregnant twins during the breeding season. Although pregnancy-related reductions in yields of milk, milk fat, and milk protein occurred after midgestation, overall effects of pregnancy on milk production in this pasture-based, seasonal calving system were small.

Animals↗
PubMed2003

Dietary cation-anion difference and the health and production of pasture-fed dairy cows. 1. Dairy cows in early lactation.

Diets offered to lactating dairy cows in the pasture-based dairy systems in southeastern Australia can vary in their dietary cation-anion difference (DCAD) from 0 to +76 mEq/100 g. The effects of such a range of DCAD on the health and production of cows, on a predominantly pasture-based diet, were examined in an indoor feeding experiment. Four groups of five cows were offered a diet of 5 kg of barley and ad libitum pasture, which is a diet representative of what is offered to cows in early lactation in the region. The cows were supplemented twice daily, with varying levels of salt combinations to alter the DCAD, which ranged from +21 to +127 mEq/100 g. Although a reduction in DCAD to +21 mEq/100 g caused a nonrespiratory systemic acidosis, there was a threshold value, above which blood and urine pH did not appear affected, although the strong ion difference of blood and urine and the blood bicarbonate concentration increased linearly (P < 0.05, 0.001, and 0.01, respectively). A DCAD above +21 mEq/100 g linearly reduced dry matter intake (P < 0.1), average daily bodyweight gain (P < 0.05), and milk protein yield (P < 0.05) but did not have a significant effect on the concentration of fat, protein, or lactose in milk. Although data were consistent with a tendency for milk yield to decrease as dietary cation-anion differences increased, this trend was not statistically significant. Urine hydroxyproline to creatinine ratio increased (P < 0.001) as dietary cation-anion difference increased, possibly suggesting an increased rate of uterine involution. It is concluded that a range in the dietary cation-anion difference, above +52 mEq/100 g, may have deleterious effects on dry matter intake and milk production.

Animal Nutritional Physiological Phenomena↗
PubMed2003

Dietary cation-anion difference and the health and production of pasture-fed dairy cows 2. Nonlactating periparturient cows.

Anecdotal observations of reduced hypocalcemia due to small reductions in the precalving dietary cation-anion difference (DCAD) are widely reported in Australia and New Zealand. Diets offered to nonlactating, periparturient dairy cows in pasture-based dairy systems in southeastern Australia can vary in their cation-anion difference from 0 to +76 mEq/100 g. The effects of such a range in the DCAD on the health and production of cows, on a pasture-based diet, were examined in an indoor feeding experiment. Four groups of four cows were offered pasture-hay and freshly cut pasture, a periparturient diet typical of that associated with the grazing system in Australia and New Zealand. Varying levels of salt supplementation were used to alter the dietary cation-anion difference, which ranged from -12 to +69 mEq/100 g. Blood and urine pH and mineral concentrations and urine hydroxyproline were measured. The addition of anions to the diet, to produce a negative DCAD, resulted in a nonrespiratory systemic acidosis. With decreasing DCAD, the pH of blood and urine and the strong ion difference of urine decreased curvilinearly, blood bicarbonate decreased linearly and the urinary ratio of Ca to creatinine increased curvilinearly. Although systemic pH was not reduced at a DCAD of +16 mEq/100 g, urine Ca-to-creatinine ratio had begun to rise, probably indicating increased calcium absorption. The absorption and renal excretion of Mg increased with decreasing DCAD. No differences were observed in urine hydroxyproline concentrations and no significant differences in milk production were measured.

Animal Feed↗
PubMed2003

A low dietary cation-anion difference precalving and calcium supplementation postcalving increase plasma calcium but not milk production in a pasture-based system.

It was hypothesized that a reduction in the dietary cation-anion difference (DCAD) before calving, combined with an increase in Ca intake after calving, would reduce the incidence of periparturient hypocalcaemia and increase milk production in pasture-based dairy cows. Cows (n = 40) were assigned to one of two DCAD levels before calving (i.e., +7 and +50 mEq/100 g). Each group was then assigned to one of two dietary Ca concentrations after calving (i.e., 1.0 and 0.7%) in a 2 x 2 factorial design. The lower DCAD resulted in a nonrespiratory reduction in systemic pH as indicated by a lower urine pH. This acidosis resulted in an increased concentration of Ca in urine before calving. The lower precalving DCAD helped prevent the decline in blood Ca caused by the onset of lactation, even though blood Ca concentration was lower before calving compared with cows receiving a high DCAD. Supplementation of cows with Ca after calving increased plasma Ca concentration on the day of calving and during the subsequent 14 d. Milk production was not affected by pre- or postcalving treatments.

Animal Feed↗
PubMed2003

Energy nutrition of the pasture-based transition cow--a review.

A restriction in energy intake during the final weeks pre-calving is believed to depress milk production post-calving. The requirements of the non-lactating periparturient cow for energy, and in particular for glucose, have been shown to increase dramatically as parturition approaches. However, a decline in precalving dry matter intake has also been measured during this period. One solution to this problem has been to reduce the forage to concentrate ratio, thereby substituting feeds that are greater in energy density for feeds that are less dense. However, the pre-calving decline in dry matter intake appears greater as the amount of concentrates in the diet increases or alternatively as the fibre concentration of the diet declines. Previous reviews of transition cow nutrition have largely dealt with the nutrition of cows offered a total mixed ration or diets containing primarily lucerne or maize silage, and have not accounted for differences in farming systems, the base diet offered, or differences between cows within breeds. In this paper the effect of nutrition during the transition period on the metabolism of the periparturient cow offered a pasture-based diet was examined.

Animal Feed↗
PubMed2003

Hypocalcaemia and DCAD for the pasture-based transition cow--a review.

Hypocalcaemia or milk fever is a condition resulting from an insufficiency of plasma calcium to maintain proper body function and is probably the most prevalent mineral-related disorder faced by the transition cow. It is also referred to as parturient paresis or parturient paralysis due to the recumbency that accompanies the most common hypocalcaemia, that is hypocalcaemia that occurs at or around calving. Milk fever was first reported in Germany in 1793 and since then has been the study of many researchers because of its economic importance, reducing milk production by 7 to 14%, depending on the degree of severity. Its prevention has been addressed by different methods including deliberately changing the blood acid-base balance through supplementation of metabolically strong anions (chlorine and sulphur) in an attempt to improve calcium homeostasis in the periparturient cow. This adjustment to the systemic acid-base balance of the cow is difficult to achieve practically and consistently in pasture-based systems and recent research has questioned its efficacy in maintaining a periparturient eucalcaemia.

Animal Feed↗
PubMed2003

The incidence and control of hypocalcaemia in pasture-based systems.

A large emphasis on precalving magnesium supplementation has substantially reduced the incidence of clinical hypocalaemia in pasture-based systems. Survey data in the major pasture-based systems suggest a 2 to 4% incidence of parturient paresis, although this can vary considerably between farms. Detailed blood measurements under research conditions suggests that approximately 5% of cows are clinically hypocalcaemic (blood calcium < 1.4 mmol/l) and between 30 and 40% of cows are subclinically hypocalcaemic (plasma calcium < 2.0 mmol/l). Systems of control have traditionally been based on preventing the paretic cow, with more emphasis of late being placed on preventing hypocalcaemia. Preventative measures vary, but largely involve either supplementation with magnesium oxide pre-calving, supplementation with calcium carbonate during the colostrum period or a combination of magnesium supplementation precalving and calcium supplementation post-calving. In New Zealand, the use of commercial products that bind calcium is increasing precalving, but is still only practiced by a small percentage of farmers. The dietary cation-anion difference (DCAD) of pasture is so high and so variable that changes in DCAD sufficient to change blood pH are not practical and very difficult to achieve with consistency. The use of magnesium chloride and magnesium sulphate in preference to magnesium oxide, as precalving magnesium supplements, is increasing.

Animal Husbandry↗
PubMed2002

Sulfur and chlorine play a non-acid base role in periparturient calcium homeostasis.

The increased risk of periparturient hypocalcaemia through offering high-K feeds in the precalving period has been reported previously. Two experiments (experiment 1 and 2) investigated the effect of KCl fertilizer on pasture mineral concentration, the dietary cation-anion difference (DCAD), and the subsequent effect of this on periparturient plasma and urine mineral status. Experiment 2 examined the effect of precalving Mg source (MgO, MgSO4, and MgCl2) and postcalving Ca supplementation on the concentration of Ca and Mg in plasma and urine. Unexpectedly, pasture DCAD increased (P = 0.06) from 434 to 535 mEq/kg DM in experiment 1 as pasture K concentration decreased from 4.2 to 3.5%, primarily because of a corresponding and greater decrease in pasture Cl concentration (from 1.9 to 1.3%). Plasma Ca or Mg concentrations were not affected by pasture K concentration. A linear decline (P < 0.10) in urine Mg suggested a decline in Mg absorption as pasture K increased. In experiment 2, pasture DCAD decreased (P < 0.05) linearly from 403 to 350 mEq/kg DM as pasture K concentration decreased from 3.8 to 3.3%. However, precalving urine pH was not affected by the declining DCAD. Postcalving plasma Ca concentration was affected by precalving Mg source with MgSO4 > MgCl2 > MgO. Differences in acid-base balance do not explain the difference between Mg salts. These results indicate that precalving dietary S and Cl concentration plays an important role in Ca homeostasis, in addition to its role in acid-base balance. Supplementation with Ca postcalving increased plasma Ca concentration for 2 d postcalving. Milk production was not affected.

Animals↗