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Biomedical subjects

K L Macmillan

Publications and source records attributed to K L Macmillan.

At least 73 records · Page 4Linked to original sources
PubMed1995

Physiological effects of undernutrition on postpartum anoestrus in cows.

The focus of this review is the physiological effects of undernutrition on ovarian follicle growth and the occurrence of ovulation in postpartum cows. Evidence suggests that moderate levels of underfeeding, before or after calving, may interfere with the mechanism(s) of final follicle maturation and ovulation, whereas more pronounced nutritional deficiencies may affect the mechanism(s) regulating dominant follicle size and the dynamics of dominant follicle growth and regression. Severe undernutrition may result in the absence of follicles > 5 mm in diameter. These changes are consistent with likely effects of reduced LH or FSH secretion that have been associated with inhibition of both tonic and surge release of GnRH from the hypothalamus. As yet, there is no direct evidence for local effects of undernutrition on ovarian function in cows, and studies examining this tissue often ignore dynamic interdependencies between the hypothalamus, anterior pituitary gland, and the ovaries, and possible nutritional modulation of ovarian feedback mechanisms that affect gonadotrophin secretion. Further research is required to elucidate nutritional effects on the positive feedback regulation of gonadotrophin secretion and on the expression of behavioural oestrus. Further studies are also needed to determine whether nutritional or metabolic state may influence ovarian function directly in a manner that affects the duration of postpartum anoestrus and fertility in postpartum cows.

Anestrus↗
PubMed1994

Adrenal cortex response to adrenocorticotropic hormone in dairy cattle.

Adult dairy cows were treated with a range of doses (0.0125mg to 0.4mg) of synthetic ACTH1-24 and the plasma cortisol response was measured. Peak response was independent of dose. Higher doses of ACTH had a more prolonged effect such that the integrated response was dose dependent. Dose response curves were examined by regression analyses. Individual cows had a significant effect on y-axis intercept but not on the slope of the regression lines examined. A dose rate of 0.05mg ACTH iv was identified as a suitable dose rate for use in clinical assessment of adrenal cortex function, with 0, 50 and 120 min following ACTH being critical sampling times to identify the response.

Adrenal Cortex↗
PubMed1994

Concentrations of oestrone sulphate during pregnancy in milk from Jersey and Friesian dairy cows differing in milk yields and composition.

Oestrone sulphate concentrations were measured by radioimmunoassay in milk samples obtained weekly during pregnancy from Jersey and Friesian cows, with each breed grazed at two different stocking rates. Mean milk yields differed significantly (P<0.05) between the four herds, while mean percentage milk fat and protein values differed significantly (P<0.05) between the two breeds. In all four herds, oestrone sulphate concentrations in milk rose progressively during pregnancy from a mean value of approximately 80-100 pg/ml at 60-80 days of pregnancy to a plateau value of approximately 1 ng/ml at 181-200 days. In non-pregnant cows, oestrone sulphate concentrations in milk ranged from non-detectable to 110 pg/ml, with a mean +/- s.e.m. value of 59 +/- 4 pg/ml. There was considerable variation in milk oestrone sulphate concentrations between cows in each herd, and oestrone sulphate concentrations could also fluctuate markedly within cows from week to week. Despite this variation, the concentration of oestrone sulphate in 98% of milk samples obtained after 120 days of pregnancy was greater than the highest concentration found in milk from non-pregnant cows. Measurement of oestrone sulphate concentrations in milk samples taken at least 120 days after mating or insemination may provide an alternative, non-invasive means of determining or confirming pregnancy in New Zealand dairy cows.

Journal Article↗
PubMed1994

Variation in selected blood plasma constituents during the post-partum and breeding periods in dairy cows.

Concentrations of insulin-like growth factor-I, albumin, beta hydroxybutyrate, glucose and urea were measured in 12 plasma samples collected over 9 weeks from mid-August from each of 40 cows in four seasonal herds which calved from mid-July. These herds comprised Jersey or Holstein-Friesian animals, with each breed grazed at two stocking rates. Daily dry matter intakes (kg dry matter/cow/day), which were estimated from pasture assessments before and after grazing, ranged from 4% (low stocked Jersey herd) to 38% (high stocked Friesian herd) below recommended intakes for each breed of cow in peak lactation. Stocking rate was associated with a 4% reduction in liveweight for cows in the high stocked herds and a 20% reduction in daily milk production (as a proportion of the low stocked herds' liveweight and milk production). Eight cows produced at least one blood sample with a beta hydroxybutyrate concentration of more than 1.0 mmol/l. There were 42% of samples with glucose concentrations greater than 4.1 mmol/l. These two concentrations were the maximum values classified as normal for these two metabolites by the Ruakura Animal Health Laboratory. No concentrations of the other metabolites were outside their respective normal ranges. Breed, age and individual animals usually had greater effects on the average metabolite concentrations than did stocking rate. The greatest effect was associated with sample day, especially for insulin-like growth factor-I and urea. A significant breed x stocking rate x sample day interaction in urea concentrations indicated that changes in the feeding value of the grazed pastures available to each herd were sufficient to produce separate fluctuating patterns in the daily average concentrations. These results showed that frequent sampling on a herd basis would be necessary to identify the significance of factors which may be contributing to sample day variation in the concentration of metabolites in the plasma of pasture-fed cows.

Journal Article↗
PubMed1991

Effects of an agonist of gonadotropin-releasing hormone on ovarian follicles in cattle.

Three experiments were conducted to examine effects of Buserelin, a potent agonist of gonadotropin-releasing hormone, on characteristics of ovarian follicles in cycling cows and heifers. In experiment 1, heifers were injected once with 10 micrograms Buserelin on Day 11, 12, or 13 of the estrous cycle (estrus = Day 0), or once with 20 micrograms of Buserelin on Day 12. Additionally, two groups were injected with a luteolytic dose of prostaglandin F2 alpha (PGF2 alpha) on Day 13 preceded with or without a Buserelin injection (10 micrograms) on Day 12. A control group did not receive a Buserelin injection. Ovaries were recovered and weighed after animals were slaughtered on Day 15. Follicle diameters were measured with calipers. Follicles for all experiments were classified as small (class 1: 3-5 mm diameter), medium (class 2: 6-9 mm), or large (class 3: greater than 9 mm). Heifers receiving only Buserelin had an increased number of medium-sized follicles compared to controls. Buserelin injection administered 24 h before PGF2 alpha reduced the decline in the average weight of the ovaries containing the corpus luteum (7.8 g for Buserelin before PGF2 alpha vs. 6.7 g for no Buserelin before PGF2 alpha). Buserelin pretreatment appeared to delay or prevent complete luteolysis by the injected PGF2 alpha. In experiment 2, 0, or 10 micrograms Buserelin was injected on Day 12 and follicle development was monitored by ultrasonography in situ from Day 12 to estrus. Follicles also were classified as clear or cloudy; cloudy was associated with flocculent material in the follicular fluid or with an indistinct follicular wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effect of timing of prostaglandin PGF 2 alpha injection subsequent to embryo collection on the resumption of normal follicular development following superovulatory treatment in cattle.

Nonlactating Holstein and Jersey cows (n = 24) were superovulated and ovarian follicular development was monitored by transrectal ultrasound during the period after embryo recovery. Luteolysis was induced by two injections of prostaglandin F(2)alpha (PGF; 25 mg Lutalyse; 12-h interval) at specific times after superovulatory induced estrus (Treatment 1, Day 9; Treatment 2, Day 12; Treatment 3, Day 17; Treatment 4, Day 25; superovulatory estrus = Day 0 of Cycle 1). Follicular development was monitored during Cycle 1 before and after PGF injection and continued through the ensuing estrous cycle (Cycle 2). Superovulation led to more than one embryo collected in 14 cows (mean = 8.71 embryos: positive superovulatory response [PSR] cows), while 10 cows were not successfully superovulated (mean = 0.1 embryo; negative superovulatory response [NSR] cows). These cows differed in terms of number of unovulated follicles detected at embryo collection (4.21 vs 17.2, PSR vs NSR) and plasma progesterone during the superovulatory estrous cycle (32.3 ng/ml PSR vs 8.6 ng/ml NSR). Follicular development during Cycle 1 started sooner in NSR than in PSR cows (day by class by response P<0.03) and was initiated on Days 11 to 12 in NSR cows and on Days 19 to 20 in PSR cows. Interval to estrus after PGF averaged 6.3 d. Cows having short intervals to estrus had follicles at the time of PGF injection. Treatment influenced the length of Cycle 1, but it did not affect the interval to estrus after PGF, the length of Cycle 2, or follicular development during Cycle 2. The results indicate that 1) the timing of PGF injection after embryo collection does not influence subsequent follicular populations, 2) elongated estrous cycles and intervals to estrus after PGF in superovulated cattle are a function of decreased follicular activity, and 3) the presence of numerous corpora lutea and not the superovulatory treatment, per se, seem to attenuate follicular growth.

Journal Article↗
PubMed1990

Calving patterns in seasonal dairy herds.

Two field studies examined the calving patterns of cows in seasonal dairy herds in the Waikato (Field Study 1) and South Taranaki regions (Field Study 2). The first study examined patterns for cows commencing their second or subsequent lactation in herds which had used an inseminating service during the previous season. The second study included first lactation heifers only in 15 herds where animals had been naturally mated, and in 15 herds in which they had been synchronised and then artificially inseminated at the synchronised oestrus. The parameters describing calving patterns were based on the date for each herd's planned start of calving (PSC), which was 282 days from the date on which breeding commenced in the preceding season. The average interval from PSC to mean calving date for the 35 herds in Field Study 1 was 22 days, with individual herds ranging from 15 to 30 days. In herds with heifers which had been naturally mated (Field Study 2), it was 17.6 days compared to 11.0 days for previously synchronised animals. Calculating the intervals from PSC to median calving date and separately for the last two quartiles more effectively described a herd's calving pattern. The duration for the last quartile of the calving pattern was influenced by the extent and timing of induced calving. In Field Study 1, 88.6% of the 35 herd owners induced premature parturition in at least one cow. In these herds, 11.3% of cows were treated and calved prematurely. Only 61.7% of heifers which had previously been naturally mated calved by 3 weeks after PSC. Their calving dates were not evenly distributed over this 3-week period, with 9.8% in the first week and 25.6% in the third week. The calving pattern for heifers which had been previously synchronised showed several distinct peaks. Calvings to the synchronised mating were completed 15 days after PSC, by which time 64.7% of animals had calved. By 3 weeks after PSC, 72.9% of these heifers had calved. The results showed that there was considerable variation in calving patterns in seasonal dairy herds. This variation would have been due to differences in conception pattern, and the way induced calving had been applied. The calving pattern in heifers which had been naturally mated was less concentrated than had been expected. Synchronisation can significantly concentrate the calving pattern of these first lactation animals. The parameters used to describe calving patterns may be less applicable in herds in which a high proportion of animals is induced to calve prematurely, or where a whole herd is synchronised. Nonetheless, they do serve as an illustrative example of the variation in calving patterns among herds.

Journal Article↗
PubMed1988

Detecting estrus in synchronized heifers-using tailpaint and an aerosol raddle.

A synchronization treatment was initiated when each of 1227 heifers (four trials) was tailpainted. The tailpaint was sprayed with an aerosol raddle at the end of the treatment period. The heifers were in herds of 20 to 279 animals. Each herd was observed for estrus at selected post treatment intervals. A heifer was considered to be (or to have been) in estrus when the raddle was rubbed off. In three of the trials, animals which had the raddle removed were inseminated at 48 h following the end of the synchronization treatment. The tailpaint of an inseminated animal was scored from 0 (less than 10% of the paint remained) to 5 (more than 90% of the paint remained) and was then reraddled with a second color. The detection-insemination sequence was always repeated at 72 and 96 h, and sometimes at 120 h. Animals which had been previously inseminated, but then had paint scores reduced by at least 2 units were reinseminated 24 h later. Over the four trials, 94.5% of the heifers were detected in estrus through the use of the tailpaint and raddle system. The remaining 67 animals included only 10 (0.8%) which had ovulated without being detected in estrus. The reinsemination rate on consecutive days was 11.3% and was highest among animals that had a tailpaint score of 4 or 5 at 48 h. The proportion of animals detected in estrus at selected posttreatment intervals varied with the different synchronization treatments used within one herd, or with the same treatment used in different herds. The combination of tailpaint, raddling, tailpaint scoring and reraddling is a simple sequence which can be effectively used to detect estrus among heifers synchronized in research or commercial herds.

Journal Article↗
PubMed1986

Induction of oestrus and ovulation in anoestrous fallow deer (Dama dama) by using progesterone and GnRH treatment.

Fourteen seasonally anoestrous, non-lactating fallow does were each treated with an intravaginal progesterone device for 14 days followed by a subcutaneously implanted osmotic minipump delivering synthetic GnRH at doses of 125 ng/h (7 does) or 250 ng/h (7 does) for up to 7 days, about 6 weeks before the natural breeding season. One doe (low delivery rate) lost its intravaginal device and 6 of the remaining does (46.2%) exhibited oestrus between 71 and 120 h after progesterone withdrawal/minipump insertion. Only one of these does received the low GnRH delivery rate and 5 received the high rate. Serum progesterone profiles indicated that an induced oestrus was followed by apparently normal luteal development. Does which did not exhibit oestrus failed to show a luteal response. Only 1 doe conceived at induced oestrus, producing a viable female fawn 6 weeks before the start of the natural fawning season. The remaining does returned to an anoestrous state until the onset of the natural breeding season.

Animals↗
PubMed1984

LH concentrations in two cattle with XY gonadal dysgenesis.

Two animals with XY gonadal dysgenesis both had a reproductive tract similar in size to that found in sexually immature heifers, but neither had normal testicular or ovarian tissue. All cells examined in both animals contained XY chromosomes and spinal cord neurones were sex chromatin negative. Basal LH concentrations averaged 3.1 ng/ml in Animal 1 and 2.4 ng/ml in Animal 2 but increased within 12 h of injecting oestradiol to peak concentrations of 125 and 11 ng/ml respectively. Animal 1 displayed a distinct pulsatile LH release pattern with a highly repeatable decline phase at each pulse. A GnRH injection produced a rapid rise in plasma LH in both animals, sustained in Animal 1 at greater than 500 ng/ml for more than 2 h. Each animal displayed behavioural symptoms of oestrus within 12 h of being injected with 3 mg oestradiol benzoate and was repeatedly served by a bull. These studies indicated that both animals differed from freemartins and had some hypothalamic and pituitary response patterns resembling those reported for female cattle.

Animals↗
PubMed1983

Prostaglandin responses in dairy herd breeding programmes.

A re-evaluation of results from ten trials conducted in commercial dairy herds between 1974 and 1981 in which lactating dairy cows were injected once or twice with either of two forms of prostaglandin F2alpha (PGF) showed that: the variation in the post-injection interval to oestrus was influenced by the stage of the oestrous cycle at which treatment was administered; this variation was sufficient to reduce pregnancy rates to set-time inseminations; an accurate aid for oestrus detection, such as tail painting, should be used routinely with PGF; if PGF-treated cows were detected in oestrus before being inseminated, the pregnancy rates to first insemination were usually 10% higher than in untreated herd mates. The results show that PGF systems in dairy herds should not be used as au alternative to accurate oestrus detection. These systems can be used to condense the breeding programme and increase pregnancy rates to first insemination. The exploitation of this fertility effect justifies the reassessment of PGF usage in New Zealand dairy herds.

Journal Article↗
PubMed1982

Prostaglandin F(2alpha) - A fertility drug in dairy cattle?

Lactating dairy cows were injected once or twice with the Tham salt or an analogue of prostaglandin F(2alpha) (PGF) in a series of nine trials. In specific comparisons involving only those cows observed in estrus during the 24 h before they were inseminated, the average pregnancy rate to first insemination for over 2000 PGF treated cows was 69%, compared to 60% in a comparable number of untreated herd mates. The one trial in which this fertility effect did not occur was one in which semen of low fertility was used only with PGF treated cows. Exploitation of this fertility effect associated with the use of PGF requires accurate diagnosis of estrus. This is necessary because of variation in the interval from injection to estrus and can be achieved by the use of tail paint. This simple technique also allows single PGF injection regimens to be successfully used. The fertility advantages associated with the use of PGF have also been reported by others but may not have received due recognition because of the quest for a procedure which dispensed with the need for estrus detection.

Journal Article↗
PubMed1977

Effects of low concentrations of cetyltrimethylammonium bromide on diluted bovine spermatozoa.

Cetyltrimethylammonium bromide (CTAB) at a concentration of 10 mg/l in a citrate buffer partially protected sperm against the effects of cold shock treatment. CTAB concentrations of 10 and 20 mg/l also increased in vitro sperm livability when semen was diluted in Caprogen and incubated at 37 degrees C (50 h v. 60 and 57 h). Concentrations of CTAB exceeding 50 mg/l reduced in vitro sperm livability. The addition of catalase (4.5 mg/l) to Caprogen produced greater increases in in vitro sperm livability (50 h v. 110 h), but did not eliminate the toxic effect of the higher CTAB concentrations. The addition of CTAB (10 mg/l) to the Caprogen-catalase diluent significantly increased the non-return rate of the diluted semen in only one of four large-scale field trials and did not alter non-return rates with deep-frozen semen.

Animals↗