Short communication: Feed restriction around insemination did not alter birth sex ratio in lactating dairy cows

The female to male calf sex ratio is associated with the number of services to achieve a calf and parity of lactating dairy cows

Commercial dairy producers may get frustrated by the lower ratio of female to male calves born because female calves are more valuable than bull calves. Our objective was to determine if parity or stage of lactation at the time of breeding, using conventional semen, influenced the sex of the calf. Data from the University of Illinois and the University of New Hampshire dairy herds were collected and summarized for calf sex, the number of services to achieve a calf and the lactation number when conception of that calf occurred. Logistical regression procedures were used to analyze the dataset via version 9.4 of SAS. The final dataset contained 2,987 calvings, which consisted of 1,406 females and 1,581 males (47.1% and 52.9% for females and males, respectively). The frequency distribution of the number of services to achieve a calf was highest for the first service and progressively declined with increasing services (52.06%, 21.66%, 10.75%, 6.66%, 4.22%, and 4.65% for 1 to 6 services, respectively). The frequency distribution of calvings by lactation number was greatest for first lactation cows becoming pregnant with their second calf and declined with increasing parity (35.49%, 28.22%, 17.01%, 9.61%, 5.02%, 2.51%, 1.14%, 0.70%, and 0.30% for lactation numbers 1 to 9, respectively). Logistic stepwise regression indicated that the number of services to achieve a calf was significant in predicting the ratio of female to male calves. Calculation of odds ratios indicated that as the lactation number increased the likelihood of getting a bull calf decreased. Parity, services, and parity by services interaction were significant for cows having a greater number of parities and cows with a greater number of services yielding more heifer calves. However, an interaction occurred where cows with greater number of services along with greater parities more likely to have a bull calf. These data provide evidence that increasing the number of services to achieve a calf and increasing age of the cow increased the probability of a heifer calf being born. These data indicate that cows with greater parties (lesser cull rate) are more likely to produce heifer calves.

Holsteins favor heifers, not bulls: biased milk production programmed during pregnancy as a function of fetal sex

Mammalian females pay high energetic costs for reproduction, the greatest of which is imposed by lactation. The synthesis of milk requires, in part, the mobilization of bodily reserves to nourish developing young. Numerous hypotheses have been advanced to predict how mothers will differentially invest in sons and daughters, however few studies have addressed sex-biased milk synthesis. Here we leverage the dairy cow model to investigate such phenomena. Using 2.39 million lactation records from 1.49 million dairy cows, we demonstrate that the sex of the fetus influences the capacity of the mammary gland to synthesize milk during lactation. Cows favor daughters, producing significantly more milk for daughters than for sons across lactation. Using a sub-sample of this dataset (N = 113,750 subjects) we further demonstrate that the effects of fetal sex interact dynamically across parities, whereby the sex of the fetus being gestated can enhance or diminish the production of milk during an established lactation. Moreover the sex of the fetus gestated on the first parity has persistent consequences for milk synthesis on the subsequent parity. Specifically, gestation of a daughter on the first parity increases milk production by ∼ 445 kg over the first two lactations. Our results identify a dramatic and sustained programming of mammary function by offspring in utero. Nutritional and endocrine conditions in utero are known to have pronounced and long-term effects on progeny, but the ways in which the progeny has sustained physiological effects on the dam have received little attention to date.

Influence of social dominance on the secondary sex ratio and factors affecting hierarchy in Holstein dairy cows

In several studies of different species, the proportions of male and female offspring did not match the statistical assumption of 50:50. Aside from environmental and genetic factors, biological parameters were found to influence the sex ratio. Three hypotheses (Trivers-Willard, advantaged daughter, and the local resource competition hypothesis) have been proposed, stating that the sex of progeny might be influenced by sex-biased maternal investment in the raising of offspring. The results of existing studies are still conflicting, even within studies on the same species. The aim of the present study was to investigate whether the dominance status of cows influences the secondary sex ratio. A herd of lactating cows was observed directly for 126 h, and a dominance index (DI) was established for 71 individuals (aged between 2.6 and 9.8 yr) for which at least 8 encounters had been observed to categorize individuals as subordinate, intermediate, or dominant. Furthermore, the number and sex of calves were assessed, and further individual characteristics of the animals (e.g., age, milk yield, body condition, and lameness scores) were analyzed for interrelationships with dominance status as well as the influence of the DI on the secondary sex ratio. The results indicated that the DI was independent of age, but a negative correlation was found between DI and lameness, whereas a positive correlation was shown for DI and body condition score. In general, more dominant animals had lower lameness scores and better body conditions. No sex ratio bias was found for primi- or for pluriparous animals and no seasonal influences were detected. The proportion of male offspring was significantly correlated with the DI of lactating cows, where animals with a higher social rank produced a lower proportion of male progeny. The pairwise comparison between dominant and subordinate lactating cows revealed a significant difference in the sex ratios of progeny, with subordinate animals having more male calves. These results indicate that the maternal dominance rank was associated with the secondary sex ratio in cattle. These observations are generally in agreement with the advantaged daughter hypothesis.