PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Reproductive performance”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

Parotid gland enlargement and female reproductive performance in a Papua New Guinea highland population.

Swelling of the parotid salivary glands is commonly observed among males and females of highland Papua New Guinea. Evidence suggests that the condition is related to the highlanders' high starch consumption in the form of sweet potato. In this paper we regard parotid enlargement as an indicator of high energy intake and test its association with two measures of reproductive performance, the number of live births and living offspring, in a sample of 274 women from Lufa in the Eastern Highlands District of Papua New Guinea. Multiple regression analysis including maternal age showed that parotid enlargement is positively correlated with both measures of reproductive performance. Given that parotid gland enlargement in this population is due to persistent starch consumption, and that the condition represents above average energy intake, these results suggest that increases in energy intake relate to increases in reproductive performance in this sample of highland females.

Adult↗
PubMed2004

Habitat quality as a predictor of spatial variation in blue tit reproductive performance: a multi-plot analysis in a heterogeneous landscape.

Vertebrate studies have rarely investigated the influence of spatial variation in habitat richness on both short-term (breeding) and long-term (offspring recruitment) reproductive performance using simultaneously multi-patch, multi-habitat type and multi-year approaches at landscape level. Here we present results of such an approach using the influence of two oak tree (Quercus ilex, Q. humilis) species on reproductive performance in Corsican blue tits (Parus caeruleus ogliastrae) as a model system. We found that blue tits breeding in rich broad-leaved deciduous patches consistently laid eggs earlier in the season, and produced larger clutches and more fledglings of higher quality, than those breeding in poor evergreen patches. Also, parents, especially males, were in better physical condition in the broad-leaved deciduous than in the evergreen patches. Surprisingly, estimates of long-term effects of reproduction, such as recruitment rates of locally born offspring, did not differ between the two habitat types. Our results suggest that short-term breeding performance and phenotypic quality of both chicks and parents do not necessarily provide reliable information about contributions to following generations at a scale larger than that of the local study plot. Differences in reproductive performance between the two oak habitat types could not be attributed to density-dependent effects, differences in levels of nest predation, or differences in age structure of the birds. We suggest that habitats that are optimal for breeding are not necessarily optimal for survival after the breeding season.

Animals↗
PubMed1997

Postpartum plasma PGF metabolite profile in cows with dystocia and/or retained placenta, and effect of fenprostalene on uterine involution and reproductive performance.

Objectives of this study were to show postpartum plasma PGF2 alpha metabolite (PGFM) profile, to clarify whether endogenous PGF2 alpha plays a certain role in the uterine involution in cows with dystocia and/or retained placenta, and to examine the effects of fenprostalene, a long-acting PGF2 alpha analog, on the uterine involution and reproductive performance of the cows with abnormal puerperium. A group of 27 cows with dystocia and/or retained placenta showed a massive release of PGF2 alpha after parturition as indicated by a rise of plasma concentrations of PGFM, significantly higher than 33 cows with normal puerperium. The duration of the elevated plasma PGFM concentrations in the cows with abnormal puerperium was shorter than that of the normal cows. In cows with normal puerperium, those showing relatively longer duration of elevated plasma PGFM levels needed a shorter period for postpartum uterine involution than the cows showing a shorter duration of the PGFM elevation (P < 0.01), while no such relationship was observed in cows with abnormal puerperium. In field trials, an administration of an exogenous PGF2 alpha, fenprostalene, at 7 to 10 days (78 cows) or 14 to 28 days postpartum (74 cows) was found to be effective in facilitating uterine involution and resumption of ovarian cyclicity, and improved reproductive performance. It may be concluded that a large amount of PGF2 alpha is released for a relatively shorter period in cows after dystocia and/or retained placenta and the elevation of PGFM is not responsible for the uterine involution. The administration of the exogenous PGF2 alpha was shown to be effective at improving the postpartum reproductive performance of cows with abnormal puerperium.

Abortifacient Agents, Nonsteroidal↗
PubMed1987

Effect of 188-day treatment with somatotropin on health and reproductive performance of lactating dairy cows.

Health and reproductive performance were observed in a lactational study involving 188 d of treatment with bovine somatotropin. Treatments commenced 84 +/- 10 d postpartum and consisted of 27 mg/d of pituitary somatotropin and 0, 13.5, 27, and 40.5 mg/d of recombinantly derived somatotropin (six cows per treatment group). Cows were high yielding (greater than 9600 kg/305 d), and somatotropin increased milk yield by 16 to 41% depending on source and dose. Somatotropin had no discernible effect on mammary health based on somatic cell count and incidence of clinical mastitis. Cows receiving somatotropin averaged 96% conception rate, 2.0 services per conception, and 116 d open, which were comparable to controls. No subclinical or clinical evidence of ketosis or milk fever was observed. Thirty-two blood chemistry and physical examination variables were examined at several intervals during the study and no adverse treatment effects of physiologic importance for any of the variables were observed. Somatotropin treatment had no discernible effect on gestation length or birth weight and growth rate (first 28 d) of calves. Milk yields for the first 60 d postpartum were compared for the period just prior to start of treatment and the lactation subsequent to treatment; no treatment effects were observed. Overall, our results for a well-managed herd demonstrate somatotropin treatment did not cause any serious health effects. However, examination of subtle health effects will require large numbers of animals treated under a range of environmental and management conditions.

Animals↗
PubMed1983

Amino acid supplementation of low-protein diets for swine: effects of gestation treatment on reproductive performance of gilts and sows.

The effect of lysine and tryptophan addition to an all-corn diet fortified with vitamins and minerals fed to gestating gilts and sows was studied in a series of five trials. The experiments were designed to establish the effect of the addition of the two amino acids on: 1) N balance, 2) reproductive performance over two consecutive parities and 3) the immune response of the gestating gilt and transfer of immune proteins to the nursing pig. Nitrogen retention by gravid gilts fed an all-corn gestation diet increased (P less than .05) in response to lysine addition, but was not affected by subsequent addition of tryptophan. Daily N retention of gravid gilts fed the corn or corn and amino acid-supplemented diets was lower than that of gilts fed a 12% crude protein (CP) diet. Reproductive performance for two parities, as evaluated by gestation and lactation weight gain and, number and weight of pigs at birth and at 28 d was similar among treatments. Evaluation of the amino acid status of gestating gilts by measurement of the development of specific antibody response to sheep red blood cells and bovine serum albumin showed a trend for improved antibody development in gilts fed corn diets supplemented with both lysine and tryptophan and in the passive immunity of their offspring. Total whey protein and globulin content of 0-h colostrum was not affected by dietary treatment. The lack of a depression in reproductive performance of gilts fed an all-corn diet could be because of compensatory N retention. During the 4 to 5 d before parturition, all gilts were fed the 12% protein control diet. Gilts that were fed a corn diet from d 1 to 108 of gestation retained 40% more (P less than .01) N from d 109 to 114 of gestation than gilts that had been fed the 12% protein diet throughout gestation.

Animal Feed↗
PubMed1994

Comparison of reproductive performance in Belgian dairy and beef cattle.

A computerized program was written to collect, evaluate and compare reproductive performance data of 2004 beef (Belgian Blue breed) and 1649 dairy (Friesian Holstein and German Red) cattle in 35 Belgian herds (6 suckler beef herds, 9 milked beef herds and 20 dairy herds). Reproduction data were collected at monthly herd health visits. No difference in age at first calving was observed. Significant differences were observed among the 3 kinds of herds, and the best results were obtained in dairy herds for the calving interval, interval from calving to the first estrus, interval from calving to the first service and average number of days open. Concerning these parameters, first calvers had lower results than multiparous cows, mainly in suckler and milked beef herds. Significant differences were noted in the number of services per pregnancy. Heifers that had never calved presented the highest fertility. Primiparous beef cows had higher fertility than pluriparous cows. In dairy herds, pluriparous cows had higher fertility than primiparous cows. Estrus detection was better in milked beef herds than in suckled beef and dairy herds. Suckled beef herds had the lowest incidence of metritis and ovarian cysts of the three types of herds. Rates of abortion, overall culling and retained fetal membranes were similar in all the herds. The percentage of animals removed for infertility was highest in milked beef herds and lowest in dairy herds. Because 90% of the 1159 calvings recorded in the beef herds required a caesarean section, the reproductive performance of beef cattle represent results after caesarean section.

Journal Article↗
PubMed2001

Chlorpyrifos-induced hsp70 expression and effect on reproductive performance in transgenic Drosophila melanogaster (hsp70-lacZ) Bg9.

Expression of hsp70 in the third-instar larval tissues of transgenic Drosophila melanogaster (hsp70-lacZ) following dietary exposure to organophosphate insecticide chlorpyrifos for various time intervals was investigated. Effect of the chemical on different developmental stages of the fly was also evaluated by looking at survivorship, hatchability, emergence, fecundity, fertility, and reproductive performance. Our results showed that the toxicant evokes profound cytotoxic effect as evidenced by dark blue staining in salivary gland, proventriculus, brain ganglia, and midgut in the lowest concentration of the chemical following 24 and 48 h of exposure. On the other hand, a significant increase (61%) in hsp70 expression in the above larval tissues was observed in the next higher concentration of the toxicant after 6 h exposure when compared with that of the lowest dose. A further increase in exposure time caused 100% larval mortality. Similarly, larvae exposed to higher concentrations of the toxicant, exhibited 100% mortality within 1 h of treatment. The insecticide caused a delay in emergence and a severe reduction in survivorship of the flies in a dose-dependent manner with 100% mortality within a day of exposure in the highest dosed group. A delay in emergence by 3 days was evident even in the lowest concentration of the chemical. A drastic effect of the chemical on hatchability was found in the highest dosed group with 100% embryonic mortality at post-16 stage of the embryo. Reproductive performance was significantly affected even in the lowest dosed group. The present study suggests that certain larval tissues of Drosophila, a nontarget organism, are vulnerable to chlorpyrifos as evidenced by hsp70 expression. Further, the adverse effect of the toxicant is reflected on various stages of development of the fly including reproductive performance.

Animals↗
PubMed2006

Effect of enhancement of uterine involution and earlier initiation of post-partum cyclicity on the reproductive performance of buffalo.

The aim of the present work was to study the effect of either gonadotrophin-releasing hormone (GnRH)-prostaglandin PGF2+/--GnRH (G-P-G) or equine chorionic gonadotrophin (eCG)-PGF2+/--GnRH (eCG-P-G) regimes with or without intramuscular injection of ergometrine maleate (Methergin) within 24 h post partum on the uterine involution, initiation of post partum cyclicity and subsequent reproductive performance of buffalo. A total of 60 parturient Egyptian buffalos (2-4 lactations) were used to conduct this study. The involved animals were allotted into two main groups (A and B), each with 30 animals, on the basis of whether buffalo cows received an i.m. injection of 3 mg of Methergin within the first 24 h post partum (A, Meth. T) or not (B, Meth. NT). Each main group was subdivided into three subgroups: A1, A2 and A3 in case of A and B1, B2 and B3 in case of B. The G-P-G regime was applied on both A1 (Meth. T) and B1 (Meth. NT) buffalos, where each individual received two i.m. injections of 0.020 mg GnRH analogue (buserelin) at Days 18 and 33 post partum with i.m. injection of 25 mg PGF2+/- (Dinoprost) in between at Day 25. The eCG-P-G regime was applied on both A2 (Meth. T) and B2 (Meth. NT) buffalos, where each individual received i.m. injection of 1000 IU eCG, 25 mg of PGF2+/- (Dinoprost) and 0.020 mg of GnRH analogue (buserelin) at Days 8, 18 and 25 post partum, respectively. The A3 subgroup (Meth. T, alone) was control for A1 and A2 subgroups and the B3 subgroup was the non-treated control for all subgroups. There was a significant (P < 0.01) decrease in the days required for complete uterine involution in subgroups A1, B1 and A3, indicating the enhancement of uterine involution. The post partum cyclicity was initiated earlier in all of the treatment regimes applied in the present study, as was indicated by significant (P < 0.01) decrease in the days to first ovulation in these subgroups compared with the non-treated control subgroup. The reproductive performance of treated buffalos improved as was shown by the significant (P < 0.01) decrease in days to first service, days open and calving interval. It is concluded that enhancement of uterine involution and/or earlier initiation of post-partum cyclicity improve the reproductive performance of buffalos.

Animals↗
PubMed2001

Lack of an effect of prostaglandin injection at estrus onset on the time of ovulation and on reproductive performance in weaned sows.

We evaluated the effects of a PGF2alpha analogue on time of ovulation and reproductive performance in multiparous Camborough sows (n=47). At onset of first post-weaning estrus, sows received either an intravulval injection of 3.75 mg of prostaglandin analogue (PGF) or, served as a non-injected control (CON). Beginning 24 h after the onset of estrus, transcutaneous ultrasonography was carried out every six h to determine time of ovulation. At 36, 54, and 72 h after the onset of estrus, blood samples were taken for progesterone analysis. Weaning-to-estrus (WEI), duration of estrus, ovulation rate and number of live embryos at d 28 of gestation were recorded. Treatment had no effect (P > 0.05) on any parameters measured. Duration of estrus classified as less or greater than the overall mean also had no effect (P > 0.05) on any of the parameters measured. Results indicate that treatment did not advance ovulation nor did it improve reproductive performance in sows. Overall, a negative correlation of WEI with the ovulation rate (P = 0.0005, r = -0.54) was established.

Animals↗
PubMed2006

Postnatal development and reproductive performance of F1 progeny exposed in utero to an ayurvedic contraceptive: Pippaliyadi yoga.

Pippaliyadi yoga or pippaliyadi vati is an ayurvedic contraceptive used in India since ancient times. It is a combination of powdered fruit berries of Embelia ribes Burm.f. (Myrsinaceae), Piper longum L. (Piperaceae) and borax in equal proportion. Though the contraceptive potential is known since ancient times, no systematic developmental toxicity studies have been carried out. The present study was carried out to evaluate the postnatal developmental toxicity and the reproductive performance of the progeny exposed in utero to pippaliyadi. Pippaliyadi yoga was obtained from National Institute for Pharmaceutical Education and Research (NIPER), India and the developmental toxicity was studied by administering three doses, viz. 140, 300 and 700 mg/(kg day) to gravid females from day 6 to day 16 of gestation. Pippaliyadi did not have any adverse developmental effects with low doses, however, with the five times higher dose, a decrease in body weight of the pups was observed. The reproductive performance of the progeny born to mothers treated with pippaliyadi was not significantly affected. The present study suggests that in utero exposure to pippaliyadi does not have any adverse effect on the postnatal development and reproductive performance of the F(1) progeny.

Animals↗
PubMed1990

Growth and reproductive performance of ewe lambs fed corn or soybean meal while grazing pasture.

In a 2-yr study a total of 120 Suffolk and Suffolk-cross ewe lambs, approximately 3 mo of age, were assigned within weight strata to one of three treatments: 1) control, pasture only (C), 2) .09 kg soybean meal/(hd.d) (SBM) plus pasture or 3) .45 kg whole shelled corn/(hd.) plus pasture to compare growth and reproductive performance and to determine lamb selectivity of forage quality and type. Each year, supplements were offered from June through the 3rd wk in November. Ewe lambs were managed as one flock on Kentucky bluegrass (Poa pratensis L.) and tall fescue (Festuca arundinacea Schreb.) pastures except for a brief daily supplementation period when all lambs were brought into a corral and sorted into treatment groups for the feeding. Ewe lambs were exposed to fertile rams from October 1 through the 3rd wk of November each year. Growth rates of ewe lambs grazing pasture alone were slower than those of corn-supplemented ewe lambs and were comparable to those of SBM-supplemented ewe lambs, but reproductive performances were similar (P greater than .05). Date of first detected rise in serum concentrations of progesterone and date of first observed estrus and lambing performance were similar (P greater than .05) among treatments for each year. Compared to hand-clipped forage, forage samples collected by esophageally fistulated lambs were higher (P less than .05) in crude protein and lower (P less than .05) in acid detergent fiber each year, indicating that lambs selectively grazed higher-quality forage. These data indicate that neither protein nor energy limited growth or reproductive performance of these ewe lambs.

Animal Feed↗
PubMed2001

Body condition related to ketosis and reproductive performance in Norwegian dairy cows.

The relationships between body condition score (BCS) and ketosis, and between BCS and reproductive performance in 732 moderate yielding, dual-purpose cows were studied. The cows were of the breed Norwegian Cattle. Farms with tie-stall barns and a history of high ketosis incidence were chosen for the study. Sixteen assessors visited the farms monthly and the same assessor assigned a BCS to each cow once a month. A BCS of 3.5 or higher at calving was associated with increased risk for ketosis. Cows that subsequently developed ketosis had higher BCS than healthy cows before the disease was diagnosed, and they lost more body condition than did the latter after ketosis had occurred. Summer calving cows and primiparous cows showed the lowest risk of ketosis. A history of ketosis before first service decreased the likelihood of conception to that service. Loss in body condition during the postpartum period was associated with decreased likelihood of conception to first service, prolonged calving to conception intervals and increased number of artificial inseminations per conception. Reproductive performance was not associated with BCS at calving. We concluded that BCS is a useful method of monitoring relations among nutritional management, reproduction, and ketosis in moderate yielding dual-purpose cows.

Animal Husbandry↗
PubMed1988

Influence of concentration, duration and route of administration of melatonin on reproductive performance of spring-mated polypay and polypay-cross ewes.

The effects of exogenous melatonin on reproductive performance of 737 Polypay and Polypay-cross ewes were evaluated during a late March and April breeding period. Different concentrations (2 or 10 mg) routes of administration (fed vs implanted) and durations of administration (20 or 40 d before breeding) were studied. Estrus was synchronized in all ewes using 60 mg medroxyprogesterone acetate (MAP) in a vaginal pessary. Number of mature ewes lambing/ewe present at lambing was increased (P less than .05) nearly 20% by implanting for 40 d with melatonin (75%) or by feeding either 2 (72%) or 10 mg (73%) melatonin for 40 d before spring breeding compared with untreated control ewes (54%) or ewes implanted for only 20 d before breeding (58%). Date of lambing, number of lambs born/ewes lambing and number of lambs born alive/ewe lambing were not altered significantly by treatments. Number of yearling ewes (n = 166 for ewes 1.5 yr old at lambing time) lambing/ewe present at lambing was lower (P less than .01; 26%) than that of mature ewes (n = 381, greater than or equal to 2.0 yr; 68%). We concluded that feeding 2 or 10 mg melatonin or implanting melatonin for 40 d enhanced reproductive performance and effectively overcame the restrictions of seasonality of breeding in mature ewes. In yearling ewes, 10 mg melatonin increased the number of ewes lambing.

Administration, Oral↗
PubMed2004

Early-weaned sows: altrenogest therapy, estrus, ovulation, and reproductive performance.

Early weaning is a technique used to increase swine health status, and may cause consequences in reproductive performance of sows. An experiment was performed to evaluate these effects in a herd of sows, with weaning at 9 or 10 days post-farrowing, located in west of Minas Gerais, Brazil. Large-White sows (n=102), with three or four previous parturitions were randomly allocated to three treatment groups: T1: artificial insemination (AI) at first post-weaning estrus of the sows; T2: AI at second post-weaning estrus, T3: AI at first estrus, after an administration of a daily individual dose of 20 mg of altrenogest from 5 to 8 days post-weaning. The duration of the first post-weaning estrus did not differ among treatment groups; however, the second estrus of the T2 group was of shorter duration relative to the other treatment groups (P< or =0.035). Ovulation occurred earlier at the second estrus of the T2 group, compared with the T1 and T3 groups (P< or =0.027), being similar to that at the first estrus of T2 group (P=0.177). The relationship of the timing between ovulation and estrus was similar among treatment groups (P> or =0.221). There was no difference in farrowing rate among treatment groups (P> or =0.313). The T2 group produced a mean of 2.5 more piglets per litter (P=0.002). In conclusion, the use of altrenogest did not increase the reproductive performance of early-weaned sows.

Animals↗
PubMed2002

Effects of vaginal Brucella ovis infection of red deer hinds on reproductive performance, and venereal transmission to stags.

AIMS: To investigate the effects of vaginal Brucella ovis infection on the reproductive performance of red deer (Cervus elaphus) hinds. To determine whether stags may become infected with B. ovis by venereal transmission from mating infected hinds. METHODS: Thirty mixed-age red deer hinds serologically negative for B. ovis antibodies were synchronised for oestrus on 22 March 2000. B. ovis was inoculated into the vagina of each hind at oestrus and again, 18 days later. At oestrus, hinds were randomly allocated to six groups, each joined with a 16 month-old red deer stag seronegative for B. ovis, for 55 days. Hinds were blood sampled and scanned for pregnancy using rectal ultrasonography at monthly intervals. Six pregnant and four non-pregnant hinds were slaughtered pre-calving and three hinds were slaughtered post-calving. Reproductive tracts and foetuses were examined grossly, histologically and microbiologically. Calves were identified and blood sampled within 3 days of birth. Hinds and calves were blood sampled in February and May 2001 and vaginal swabs were collected from hinds for B. ovis culture. Blood was collected from stags, 5 and 19 days after mating and semen was collected for B. ovis culture. The 17 remaining hinds were mated in 2001 to two mixed-age wapiti (Cervus canadensis) stags. Both stags were blood sampled after mating. Sera were tested in a B. ovis complement fixation test (CFT) and enzyme-linked immunosorbent assay (ELISA). RESULTS: All 30 hinds developed B. ovis antibody levels, measurable using either the CFT or ELISA, but these did not remain elevated. There was no evidence of infection, either by gross pathology, histopathology or microbiological culture in the ten hinds or six foetuses slaughtered pre-calving. All remaining 20 hinds produced normal calves, 15 of which survived until weaning. Three hinds experienced dystocia and gave birth to dead calves and two calves died within 4 days of birth. One hind which had dystocia was euthanased. Samples from this hind and from 3/5 dead calves showed no evidence of B. ovis infection. B. ovis was cultured from the vagina of 1/19 hinds 48 weeks after inoculation, at which time B. ovis CFT and ELISA results for this hind were negative. Most calves had B. ovis serum antibodies at 1-3 days of age but levels were negligible when sampled at 10-15 weeks of age. Foetuses and dead calves were all seronegative. Three of the five red deer stags used for mating became infected with B. ovis. The two wapiti stags used to mate the remaining 17 hinds the following year remained seronegative. CONCLUSIONS: B. ovis is unlikely to have significant detrimental effects on the reproductive performance of red deer hinds. Venereal transmission via the vagina of hinds is a possible route of transmission between stags. It is possible that survival of the organism in the vagina of some hinds could create difficulties in disease control programmes. CLINICAL RELEVANCE: B. ovis infection of hinds at the time of mating is unlikely to cause significant reproductive losses. Venereal transmission of B. ovis between stags via the hinds may occur when groups of hinds are joined with more than one stag.

Journal Article↗
PubMed1999

The reproductive performance of sows after PRRS vaccination depends on stage of gestation.

In order to minimize the effects of porcine reproductive and respiratory syndrome (PRRS) on stillbirth, mummification, and neonatal mortality in swine herds, many producers have vaccinated their herds using a modified-live virus vaccine. The purpose of this study was to determine the association of the PRRS modified-live vaccine and reproductive performance by stage of gestation when the vaccine was administered. A total of 47 swine herds from Ontario and Manitoba, Canada, and from the mid-western USA were included in the study. Participating farms had vaccinated all of their sows at one point in time when they used the vaccine for the first time. The reproductive performance of sows that farrowed in the year prior to use of the vaccine was compared to that of sows vaccinated in each of five stages of gestation and in the gestation that followed the initial use of the vaccine. Sows vaccinated at any time during gestation had a reduced number of pigs born alive, a reduced number of pigs weaned per litter, and increased number of stillborn pigs and an increased number of mummified pigs compared to the sows that farrowed prior to use of the vaccine. The largest association was seen in sows that were vaccinated in the last four weeks of gestation. The largest losses were observed in those herds that were vaccinated concurrently with the initial PRRS herd outbreak. These results suggest that the modified-live vaccine should only be administered to non-gestating sows.

Animals↗
PubMed1990

Reproductive performance and variation in body weight during annual cycles for crossbred beef cows with different genetic potential for milk.

Reproductive performance and body weights were studied in 81, 79 and 88 spring-calving beef cows from three groups, reasonably similar in growth rate and mature size but different in level of milk production (low [L] = Hereford x Angus, medium [M] = Red Poll x Angus and high [H] = Milking Shorthorn x Angus). Milk group did not have a significant effect on dates of first postpartum estrus and first and last breeding or in the intervals from calving to first estrus, to first breeding and to last breeding. A significant age-of-cow x milk-group interaction was found for pregnancy rate (PR, P less than .10) and calf-crop percentage (CC, P less than .05). In heifers, PR and CC were lowest for the L (85.6 and 73.6%) and highest for the M group (94.2 and 92.5%); in 2-yr-olds there were no differences, and in older cows, PR was highest for the L (94.8%) and lowest for the H group (91.6%), and there were no differences in CC. As estimated from Brody's growth curves, mature sizes were 530 +/- 5.7, 471 +/- 4.6 and 499 +/- 4.2 kg for the L, M and H groups, respectively. Of weights taken on four occasions during the year, October weight was the highest for all cows. February weight, minus the estimated gravid uterus weight, was the lowest for L and M cows, and May weight was lowest for H cows. Weight fluctuation over an annual cycle was greatest for the L group. Under these experimental conditions, cows in all groups were able to consume sufficient energy and gain or lose body reserves to achieve similar reproductive performance while differing in lactation performance.

Animals↗