Relationships between body condition score and ultrasound skin-associated subcutaneous fat depth in equids

Background

In equids, health and welfare depend on body composition. A growing number of equids are now used as leisure and companion animals, and often found overfeed. The need for a close monitoring of body fatness led to the search for tools allowing a rapid and non-invasive estimation of fatness. This study intends to assess real-time ultrasonography (RTU) usefulness in establishing a relationship between ultrasound measures of subcutaneous fat–plus–skin thickness (SF-Skin) and body condition score (BCS) in horses and donkeys. Forty-three healthy animals (16 donkeys and 27 horses) were used in this study to generate 95 records (RTU and BCS pairs), in multiple RTU sessions for 2 years. Using visual appraisal and palpation, BCS was graded in a 1–9 points scale. Real-time ultrasonography images were taken using a 7.5 MHz linear transducer, placed perpendicular to the backbone, over the 3rd lumbar vertebra. ImageJ was used to measure the SF-Skin on RTU images. The relation between BCS and SF-Skin measurements was tested by linear and polynomial regression analysis.

Results

The BCS values were similar in horses (5.50; from 3 to 8 points) and donkeys (5.14; from 3 to 7 points). The SF-Skin measures show a similar trend (a mean of 7.1 and 7.7 mm in horses and donkeys, respectively). A polynomial regression among BCS and SF-Skin explained 92 and 77 % of the variation in donkeys and horses respectively. The coefficient of determination was considerably higher for the regression developed for donkeys compared with that of horses (R2 = 0.92 vs. 0.77, respectively), which reduced the accuracy of the method in horses. Both the linear and polynomial models tested show a strong relationship among BCS and SF-Skin for donkeys (R2 > 0.91; P < 0.01) and horses (R2 > 0.74; P < 0.01), despite that the extremes for BCS did not existed in our sample.

Conclusions

Our results showed the potential RTU usefulness to monitor body fat in equids. Using a high-frequency transducer and RTU together with image analysis allowed the identification of small SF-skin variations. This report will support further studies on the relationships between SF-Skin and BCS, particularly in extreme BCS scores.

     

Genome-wide association study identifies candidate markers for bull fertility in Holstein dairy cattle

The decline in the reproductive efficiency of dairy cattle has become a challenging problem worldwide. Female fertility is now taken into account in breeding goals while generally less attention is given to male fertility. The objective of this study was to perform a genome-wide association study in Holstein bulls to identify genetic variants significantly related to sire conception rate (SCR), a new phenotypic evaluation of bull fertility. The analysis included 1755 sires with SCR data and 38,650 single nucleotide polymorphisms (SNPs) spanning the entire bovine genome. Associations between SNPs and SCR were analyzed using a mixed linear model that included a random polygenic effect and SNP genotype either as a linear covariate or as a categorical variable. A multiple testing correction approach was used to account for the correlation between SNPs because of linkage disequilibrium. After genome-wide correction, eight SNPs showed significant association with SCR. Some of these SNPs are located close to or in the middle of genes with functions related to male fertility, such as the sperm acrosome reaction, chromatin remodeling during the spermatogenesis, and the meiotic process during male germ cell maturation. Some SNPs showed marked dominance effects, which provide more evidence for the relevance of non-additive effects in traits closely related to fitness such as fertility. The results could contribute to the identification of genes and pathways associated with male fertility in dairy cattle.     

Refinement of two female fertility QTL using alternative phenotypes in French Holstein dairy cattle

Two quantitative trait loci (QTL) affecting female fertility were mapped in French dairy cattle. Phenotypes were non-return rates at 28, 56, 90 and 282 days after insemination. On chromosome 3, a QTL was significant at 1% for non-return rate at 90 days, suggesting that it affects early fertility events. An analysis of SLC35A3, which causes complex vertebral malformation, excluded this gene from the QTL interval. On chromosome 7, a QTL was almost significant (P = 0.05) for non-return rate at 282 days. This QTL was associated with abortion and stillbirth problems. Use of appropriate phenotypes appeared important for fine-mapping QTL associated with fertility.     

Correlation between reproductive efficiency, as determined by new mathematical indexes, and the body condition score in dairy cows

The aim of this work was to study a new mathematical model based on dynamic indexes designed to evaluate reproductive efficiency in dairy herds and to correlate the new index with the body condition score (BCS) in order to evaluate the reproductive state of the cows post partum. Four groups of dairy cows were used: 1) loose-housed Italian Friesian (loose Friesian, n = 190); 2) stanchioned Italian Friesian (stanchioned Friesian, n = 121); 3) stanchioned Italian Simmental (stanchioned Simmental, n = 120); and 4) loose-housed selected Italian Friesian cows (BCS test, n = 117). The first 3 herds were used to develop the new mathematical model while the fourth was used to correlate the method with the BCS. The new model was developed from the analysis of progesterone (P4) concentrations in whey and the frequency distribution of the cows in 3 reproductive states: cyclicity, acyclicity and pregnancy. The frequency distribution generated 3 curves, the intersections of which form a closed area. The barycenter of this closed area gives a simple static representation of the reproductive efficiency of each herd. We also studied the movement of the barycenter with time (dynamic index) for each reproductive status curve. The dynamic index allowed for evaluation of the reproductive efficiency of a group of cows at 40 d after calving, by analyzing the evolution of the different reproductive states post partum. A reproductive index called Cycle Time was characterized in a 240-d period of observation as the interval needed to bring all the animals from acyclic to pregnant status. The loose Friesian cows had the best reproductive efficiency. The BCS test was used to divide cows into 3 groups depending on the percentage loss of BCS due to the negative energy balance at 30 d post partum. Cows which lost more than 20% in BCS had the lowest reproductive efficiency. The following protocol was devised to monitor herds in order to identify cows that were likely to have reproductive problems: 1) measure BCS 10 d before calving; 2) monitor progesterone in whey starting 5 d after calving; 3) measure BCS 30 d after calving; 4) isolate cows that lost more than 20% of BCS; 5) measure progesterone only in the cows that lose more than 20% of BCS; 6) activate appropriate feeding strategies to help prevent excessive mobilization of body fat reserves.     

Relationships between fertility, peak milk yields and lactational persistency in dairy cows

Peak milk yield, lactational persistency and conception rates were studied using 5928 lactation records of high milk-producing cows at three California dairies. Log-linear analysis was used to study relationships between peak milk yield, lactational persistency, dairy of origin, lactation number and conception rates in 3850 completed lactations. Cows with peak milk yields greater than the median (38.2 kg milk per day) were less likely to have conceived in one or two breedings than cows with peak milk yields lower than or equal to the median. Cows with a higher than median (0.755) lactational persistency were less likely to have conceived in one or two breedings than cows with a lactational persistency lower than or equal to the median. Dairy of origin had a significant effect on the probability of conceiving in one or two breedings. Cows in the first lactation were more likely than those in subsequent lactations to conceive in one or two breedings. This retrospective study demonstrated that subfertility is associated with high peak lactational yields in high milk-producing California cows.     

Serum post-albumins and fertility in dairy cattle

Blood samples from 180 Guernsey cows and 599 Holstein cows were typed for post-albumins (Poa). The genotypes were compared for breeding efficiency, mean return interval, anestrus interval, service interval, gestation length and lactation length. Poa SF cows had a significantly shorter (P < 0.01) mean return interval than SS cows. The effect is associated with order of insemination, but is independent of lactation number. None of the other parameters showed genotypic differences.     

Relationships between body condition score, body weight, and some nutritional parameters in plasma and resumption of ovarian cyclicity postpartum during pre-service period in high-producing dairy cows in a subtropical region in Japan

The objective of this study was to investigate the relationships among body condition score (BCS), body weight and plasma metabolite concentrations, and resumption of ovarian cycles postpartum in high-producing dairy cows in a subtropical region in Japan. The study was conducted between May 2001 and January 2003 in a commercial dairy farm in Hiroshima. Cows were kept in free-stall barns with sawdust and wood shavings for bedding, and fed a total mixed ration consisting of alfalfa, timothy and oat hay, corn, tofu ground-wet, beet pulp, cottonseed and soybean. Milk samples were collected twice weekly from 2 to 11 weeks postpartum, and progesterone concentrations in skim milk were determined by ELISA. At 8 and 2 weeks before calving and 3, 5, 7, 9, and 11 weeks after calving, both BCS and body weights were determined and blood samples were collected to determine plasma concentrations of total cholesterol (T-cholesterol), non-esterified fatty acids (NEFA), total protein, and urea nitrogen. The average 305 days milk yield was 10,422 kg. Out of 110 cows, 44.5% had normal resumption (ovulation occurred < or =45 days after calving, followed by regular ovarian cycles), 33.6% had a prolonged luteal phase (luteal activity >20 days), 12.7% had delayed first ovulation (no ovulation until < or =45 days after calving), 4.6% had a short luteal phase (luteal activity <10 days, except in the first cycle), and the remaining 4.6% had cessation of cyclicity (no luteal activity > or =14 days between cycles). The BCS of cows with delayed first ovulation were lower than the BCS of cows with normal resumption and prolonged luteal phase at 5 weeks (2.9+/-0.1 versus 3.1+/-0.1 and 3.2+/-0.1; P<0.05), 7 weeks (2.8+/-0.1 versus 3.1+/-0.1 and 3.2+/-0.1; P<0.01), 9 weeks (2.7+/-0.1 versus 3.0+/-0.1 and 3.2+/-0.1; P<0.01) and 11 weeks (2.6+/-0.1 versus 3.0+/-0.1 and 3.2+/-0.1; P<0.01) after calving. None of the plasma parameters differed (P>0.05) among different groups of cows. Cows loosing > or =1 unit BCS after calving had a prolonged interval to commencement of luteal activity, and were at greater risk of having delayed first ovulation. Poor postpartum nutritional status was associated with delayed first ovulation postpartum. Regular monitoring of BCS before and after calving would be useful in nutritional management, and help in preventing delayed first ovulation in high-producing dairy cows.     

Relationships between transition period diet,metabolic parameters and fertility in lactating dairy cows

Cows in severe negative energy balance after calving have reduced fertility, mediated by metabolic signals influencing the reproductive system. We hypothesised that transition diet could alter metabolic status after calving, and thus influence fertility. Multiparous dairy cows were assigned to four transition groups 6 weeks pre-calving and fed: (a) basal control diet (n = 10); (b) basal diet plus barley (STARCH, n = 10); (c) basal diet plus Soypass (high protein, HiPROT, n = 11); or (d) no transition management (NoTRANS, n = 9). All cows received the same lactational diet. Blood samples, body weights and condition scores (BCS) were collected weekly. Fertility parameters were monitored using milk progesterone profiles and were not affected by transition diet. Data from all cows were then combined and analysed according to the pattern of post-partum ovarian activity. Cows with low progesterone profiles had significantly lower insulin-like growth factor-I (IGF-I) and insulin concentrations accompanied by reduced dry matter intakes (DMIs), BCS and body weight. Cows with prolonged luteal activity (PLA) were older and tended to have lower IGF-I. Analysis based on the calving to conception interval revealed that cows which failed to conceive (9/40) also had reduced IGF-I, BCS and body weight. Fertility was, therefore, decreased in cows which were in poor metabolic status following calving. This was reflected in reduced circulating IGF-I concentrations and compromised both ovarian activity and conception. There was little effect of the transition diets on these parameters.     

Relationship of parity and body condition score to pregnancy rates in Florida beef cattle

Pregnancy rates, determined by per rectum palpation, were analyzed with respect to cow parity (range 1 to >8 calvings) and body condition score (BCS, 1=thin to 9=fat) at pregnancy examination for 3734 beef cattle females on 3 commercial beef operations (8 herds) in 3 Florida counties in 1989 and 1990. The means and standard deviations for the herds were the following: pregnancy rate, 81.3 +/- 39% (range 62.1 to 91.5%); BCS, 4.7 +/- 0.6 (range 4.3 to 4.9); and parity, 3.9 +/- 2.3 (range 2.8 to 4.8). Significant associations were found between pregnancy rate, parity, BCS and herd (P < 0.001); and between the variable interactions, parity with BCS, herd with BCS, and herd with parity (P < 0.001). Cows with a BCS /=5 had a pregnancy rate of 90%. Cows having a parity of <4 had a PR of 80%, while cows having a parity >/=4 had a PR of 85%. The interaction of parity with BCS was significant, resulting in pregnancy rates as follows; parity <4 and BCS /= 5 was 88%; parity >/=4 and BCS /=5 and BCS >/= 5 was 93%. Body condition, parity, and the interaction of body condition and parity play important roles in the reproductive performance of commercial beef cows in Florida.     

Relationships between cytology, bacteriology and vaginal discharge scores and reproductive performance in dairy cattle

The objective was to compare three diagnostic approaches for intrauterine infection and inflammation: scoring of vaginal contents; quantification of percentage of nucleated cells that were polymorphonuclear leukocytes (PMN) following endometrial cytology; and intra-uterine bacteriology. Dairy cows (n = 303) were examined twice, Days 28 (D28) and 42 (D42), where Day 0 = day of calving. Associations between gross vaginal inflammation scores, uterine cytology, and bacteriology, and subsequent reproductive performance were examined using multivariable models. There was fair agreement at D28 (Kappa = 0.29), but only slight agreement at D42 (Kappa < 0.15), between PMN% and gross vaginal inflammation score. Cows were categorized as having PMN% in the highest quartile (H), or not (L), at both D28 and D42; therefore, cows were categorized as PMNLL, PMNLH, PMNHL, or PMNHH. Cows in the highest PMN% quartile at both time periods were slower to conceive (P < 0.001) than those in all other quartiles (mean ± SEM 32.2 ± 2.3, 37.0 ± 5.3, 40.8 ± 4.1, and 55.3 ± 7.3 d from start of breeding to conception for PMNLL, PMNLH, PMNHL, and PMNHH PMN% cows, respectively). Milk yield was greater (P = 0.001) in cows in the lower quartiles for PMN% at D28 and D42 (i.e., PMNLL) than those in the PMNHH and PMNHL categories, with PMNLH intermediate (P = 0.001). We concluded that PMN% was a better predictor of reproductive performance than either intra-uterine bacteriology or gross vaginal inflammation score. Cows in the highest quartile for PMN% at both D28 and D42 had lower pregnancy rates, took longer to conceive, and had a lower milk yield than those in the lower PMN% categories.     

Observed frequency of monozygotic twinning in Holstein dairy cattle

Bonnier's equation is used to mathematically estimate the frequency of monozygotic (MZ) twinning in epidemiologic studies of twinning in dairy cattle; however, no empirical determination of MZ twinning has been reported in the literature. Our objectives were to empirically determine the frequency of MZ twinning in lactating Holstein cows and to compare this result with published estimates predicted using Bonnier's equation. Ear biopsies were collected from 107 sets of Holstein twins from six Wisconsin dairies resulting in 40 opposite-sex twins, 29 same-sex male twins, and 38 same-sex female twins. To empirically determine the frequency of MZ twinning, DNA extracted from ear biopsies collected from the 67 same-sex twins was PCR amplified using primers for a minimum of 5 polymorphic microsatellite DNA markers. Opposite-sex twins were classified as dizygotic (DZ) as well as same-sex twins differing in at least one microsatellite DNA marker. Same-sex twins were classified as MZ when all genotypes for a minimum of five markers were identical. Of the 67 same-sex twins, 62 were classified as DZ and 5 MZ resulting in a MZ twinning frequency of 7.5% of same-sex twins and 4.7% of all twins. The estimated frequency of MZ twinning in this population of twin calves using Bonnier's equation was 39.5% of same-sex twins and 24.7% of all twins. We concluded that MZ twinning occurred infrequently in Holstein cattle and perhaps less frequently than that reported in studies using Bonnier's equation to estimate MZ twinning.     

Management of summer infertility in Texas Holstein dairy cattle

The objectives of this study were to describe the impact of season on pregnancy odds and the effect of specific herd management practices to modify seasonal effects. Pregnancy odds were significantly associated with herd, season, days in milk, and milk production, and with 3 interactions: milk production-by-days in milk, milk production-by-parity, and season-by-days in milk. The estimate of relative risk for summer insemination resulting in pregnancy was 0.66 at 60 d post calving and 0.53 at 160 d post calving. Shade in the lounging area, holding pen or dry cow areas, and fans in the lounging area had positive effects on summer pregnancy odds. Fans in the dry cow area were associated with a reduced odds of pregnancy. Sprinklers did not significantly modify the effect of season on pregnancy odds. The strong seasonal decrease in pregnancy odds was less severe on farms that provided shade in the lounging areas, holding pens and dry cow areas and fans in lounging areas. Insemination strategies can also be adapted to increase the pregnancy odds.     

Effects of body condition score and score change on the reproductive performance of dairy cows: a meta-analysis

A meta-analysis was conducted to evaluate the effects of body condition score (BCS) at parturition and at first AI, and of body condition change during the early lactation period on the variables pregnancy rate at first AI and number of days open in dairy cattle. Inclusion criteria for the publications were: comparison of at least two groups of animals of different categories of BCS or change (independent variables) and consideration of pregnancy rate at first AI or number of days open (dependent variables). Fifteen papers were selected and 23 excluded. Data corresponding to 7733 cows from 11 studies described in 10 papers were included in the analysis of pregnancy rate at first AI, and those derived from 4529 cows from 11 studies described in 10 papers were used to analyze effects on the number of days open. Analyses were stratified according to study design and milk production characteristics. We defined low, intermediate and high categories of BCS for values lower than 2.5, from 2.5 to 3.5, or higher than 3.5, respectively. The categories of body condition change were increase (gain in score), slight loss (0-0.5 point loss), moderate loss (0.6-1 point loss), and severe loss (over 1 unit loss). Intermediate body condition at parturition and at first AI, and a slight loss during the early lactation period were used as reference categories. The effects of body condition on the variable pregnancy rate at first AI were highly heterogeneous, while all the studies considering the number of days open presented homogeneous results. A clear association between body condition category and pregnancy rate at first AI was detected only when the effect of a low score at parturition was analyzed: pregnancy rate at first AI significantly decreased by about 10% in cows delivering in poor condition. Animals with a high BCS at parturition showed a significant reduction in the number of days open of 5.8 or 11.7 when compared with animals with an intermediate or low body condition, respectively. In animals in the high body condition category at first AI, the variable days open showed a significant drop of 11.9 or 24.1, compared to animals in the intermediate or low categories, respectively. A severe loss in score during early lactation was related to a significant (10.6) increase in the number of days open, while a slight or moderate body condition change, either loss or gain in score, was not significantly related to the variable days open. We found that the number of days open was a good indicator of the effects of BCS or change in score on reproductive performance in dairy cattle. The variable pregnancy rate at first AI, however, yielded heterogeneous results among studies.     

Single nucleotide polymorphisms in the growth hormone and insulin-like growth factor-1 genes are associated with milk production, body condition score and fertility traits in dairy cows

The somatotrophic axis (GH-IGF) is a key regulator of animal growth and development, affecting performance traits that include milk production, growth rate, body composition, and fertility. The aim of this study was to quantify the association of previously identified SNPs in bovine growth hormone (GH1) and insulin-like growth factor 1 (IGF-1) genes with direct performance trait measurements of lactation and fertility in Holstein-Friesian lactating dairy cows. Sixteen SNPs in both IGF-1 and GH1 were genotyped across 610 cows and association analyses were carried out with traits of economic importance including calving interval, pregnancy rate to first service and 305-day milk production, using animal linear mixed models accounting for additive genetic effects. Two IGF-1 SNPs, IGF1i1 and IGF1i2, were significantly associated with body condition score at calving, while a single IGF-1 SNP, IGF1i3, was significantly associated with milk production, including milk yield (means ± SEM; 751.3 ± 262.0 kg), fat yield (21.3 ± 10.2 kg) and protein yield (16.5 ± 8.0 kg) per lactation. Only one GH1 SNP, GH33, was significantly associated with milk protein yield in the second lactation (allele substitution effect of 9.8 ± 5.0 kg). Several GH1 SNPs were significantly associated with fertility, including GH32, GH35 and GH38 with calving to third parity (22.4 ± 11.3 days) (GH32 and GH38 only), pregnancy rate to first service (0.1%) and overall pregnancy rate (0.05%). The results of this study demonstrate the effects of variants of the somatotrophic axis on milk production and fertility traits in commercial dairy cattle.     

Signatures of contemporary selection in the Israeli Holstein dairy cattle

Strong selection in the Israeli Holstein dairy cattle population over the last three decades should have left clear signatures of selection. Two experimental approaches were applied to detect evidence of contemporary selection based on the 54K BeadChip genotypes of ~1000 Israeli Holstein bulls: (i) the long-range haplotype test, which searches for structural evidence resulting from selective sweep, and (ii) direct analysis of the changes in haplotypes frequencies over time combined with linkage disequilibrium blocks haplotype-based association analysis. Ten traits were analyzed: the PD07 Israeli selection index, milk, milk fat, % fat, milk protein, % protein, somatic cell score, female fertility, milk production persistency and herd life. The long-range haplotype test detected ~15% of the 3288 haplotypes that showed significant positive frequency trends (P < 0.05) and was significantly correlated with the substitution effects of the haplotypes and the selection intensities for the different traits. Thirty signatures of recent selection, which correspond to both approaches and affect the Israeli PD07 selection index, were identified on 17 of the 29 autosomes. The second experimental approach also was used to estimate the selection intensity of the different traits. The correlation between the selection intensities for the traits analyzed, derived from changes in haplotype frequencies in the population of bulls, and those derived from trait-based analysis of the cow population was 0.93 over all traits. Thus, the changes in haplotypes frequencies in the bulls' population accurately estimate genetic trends in the general cow population and can be used to detect signatures of recent selection.     

Effects of body condition score on direct and indirect measurements of insulin sensitivity in periparturient dairy cows

Reductions in insulin sensitivity in periparturient dairy cows develop as a means to support lactation; however, excessive mobilization of fatty acids (FA) increases the risk for peripartal metabolic disorders. Our objectives were to investigate the effect of prepartum body condition score (BCS) on systemic glucose and insulin tolerance, and to compare direct and indirect measurements of insulin sensitivity in peripartal lean and overweight dairy cows. Fourteen multiparous Holstein cows were allocated into two groups according to their BCS at day −28 prepartum: lean (n = 7; BCS ≤ 3.0) or overweight; (n = 7; BCS ≥ 4.0). Liver biopsies were performed on day −27, −14 and 4, relative to expected parturition. Intravenous insulin or glucose tolerances tests were performed following each liver biopsy. Relative to lean cows, overweight cows exhibited lower dry matter intake, lost more BCS and displayed increased plasma FA and β-hydroxybutyrate concentrations and elevated liver lipid content during peripartum. Glucose clearance rate was lower for all cows postpartum. Prepartum BCS had minimal effects on insulin and glucose tolerance; however, the ability of the cow to restore blood glucose levels following an insulin challenge was suppressed by increased BCS. Glucose-dependent parameters of insulin and glucose tolerance were not correlated with surrogate indices of insulin sensitivity. We conclude that prepartum BCS had minimal effect on systemic insulin sensitivity following parturition. The observed inconsistency between surrogate indices of insulin sensitivity and direct measurements of insulin and glucose tolerance adds support to growing concerns regarding their usefulness as tools to estimate systemic insulin action in periparturient cows.     

Use of breed-specific single nucleotide polymorphisms to discriminate between Holstein and Jersey dairy cattle breeds

Emphasis on livestock genetic improvement in the past decades has led to commercialization of different breeds of livestock species. Breed validation has become increasingly important to assess the safety and authenticity of livestock products in global and domestic markets. The objective of this study was to evaluate the use of breed-specific single nucleotide polymorphisms (SNPs) in discriminating between Holstein and Jersey dairy cattle breeds. Two separate resource populations were used, including a reference population consisting of 498 Holstein and 83 Jersey bull DNA samples, and a validation population consisting of 260 Holstein and 34 Jersey cow DNA samples. Five Jersey-specific and four Holstein-specific SNPs were identified and genotyped on the reference and validation resource populations. The reference population was used to validate the breed-specific SNPs used in this study and to predict the allocation efficiencies and misclassification probabilities of different combinations of SNPs. Individual animals in the validation population were allocated to either breed based on the presence of breed-specific alleles. It was found that any combination of three breed-specific SNPs had, on average, high breed allocation efficiency of >95% and low misclassification probability of <5%. In conclusion, this study demonstrates a simple, yet effective, method of using breed-specific SNPs to discriminate between Jersey and Holstein cattle breeds.     

Relationships between fatty liver and fertility and some periparturient diseases in commercial Dutch dairy herds

Declining fertility in dairy cows is frequently suggested to arise from the occurrence of a more negative energy balance and/or the concomitant increased accumulation of triacylglycerol in the liver. Therefore, we performed a field study to assess the clinical effects of postpartum fatty liver in dairy cows on fertility and reproductive disease. Data were collected from 360 cows from nine dairy herds on fertility, diseases, and the liver triacylglycerol content on two occasions during lactation: 6 to 17 days and 38 to 50 days postpartum. The mean concentration of triacylglycerol in the liver was 54.6 mg/g from 6 to 17 days and 38.4 mg/g from 38 to 50 days postpartum. The probability of pregnancy was 30% lower for cows with higher contents of triacylglycerol in the liver compared to the probability for cows with low liver triacylglycerol (P = 0.049). The probability of estrus was also 35% lower for the cows with high triacylglycerol in the liver. This resulted in larger intervals between parturition and first heat and parturition and pregnancy for these cows. There was no effect observed on the first insemination conception rate. Given a certain level of triacylglycerol, recorded milk production had a positive effect on time to pregnancy. The incidences of endometritis, lochiometra and cystic ovarian follicles were not higher in cows with higher liver triacylglycerol contents. Endometritis was associated with a lower first insemination conception rate and more days open (chi2 = 4.26, P = 0.03 and T-test = -2.02, P= 0.04 respectively). We concluded that our results support the idea that differences in the negative energy balance or the accumulation of triacylglycerol in the liver of postpartum dairy cows affect fertility performance. The data also indicate that an increase in milk production has no negative impact on fertility as long as the amount of triacylglycerol in the liver remains the same.     

Endogenous hormone response and fertility in dairy heifers after treatment with Lutalyse and GnRH

Fifty-five dairy heifers were given two injections of Lutalyse 11 days apart. Twenty-one of the heifers were also given an injection of GnRH 48 hr after the second Lutalyse injection (Group G). Of the remaining 34 animals, 19 were randomly allotted to be inseminated 12 hr after observed estrus following Lutalyse (Group E), while 15 were inseminated 80 hr after the second Lutalyse injection (Group P). The intervals from second Lutalyse injection to occurrence of both estrus and peak gonadotropin concentrations were variable among animals receiving only Lutalyse. GnRH injections reduced variation (P<.01) in the interval from second Lutalyse injection to occurrence of peak gonadotropin concentrations, but did not improve fertility. Pregnancy rates did not differ (P>.05) among treatment groups. The failure of GnRH administration following Lutalyse to improve pregnancy rates indicates that GnRH administration followed by insemination 12 hr later is not effective in increasing pregnancy rates above those attained in animals inseminated at either 12 hr post estrus or 80 hr after second Lutalyse injection.