The human population is ever increasing while the quality and quantity of natural resources used for livestock production decline. This calls for improved product efficiency and the development of improved and sustainable cattle production methods to produce higher quality products to satisfy the demands of both the modern and transient world. The goal of this review was to summarize the interactions, challenges, and opportunities in cattle production relating to their endocrine system, and how reproductive hormones and others impact economically important traits, animal welfare, and human health. A comprehensive literature search was conducted with a focus on analysis of natural hormones and the use of exogenous hormone administration for reproduction, growth, and development of beef and dairy cattle. Hormones regulate homeostasis and enhance important traits in cattle, including fertility, growth and development, health, and the production of both meat and milk products. Reproductive hormones such as testosterone, estradiol, progesterone, and related synthetics like trenbolone acetate and zeranol can be strategically utilized in both beef and dairy cattle production systems to enhance their most valuable traits, but the impact of these substances must account for the welfare of the animal as well as the health of the consumer. This scientific review provides a comprehensive analysis of the bovine endocrine system’s impact on food animals and product quality which is vital for students, researchers, livestock producers, and consumers. Although important advances have been made in animal science and related technological fields, major gaps still exist in the knowledge base regarding the influence of hormones on the production and welfare of food animals as well as in the public perception of hormone use in food-producing animals. Filling these gaps through transformative and translational research will enhance both fundamental and applied animal science to feed a growing population.
The objectives of this study were to (1) evaluate the effect of rate of winter hair growth on Angus cow performance and (2) estimate the correlation between rate of winter growth and other physiological parameters. Data were collected on fall-calving Angus females (n = 127) approximately every 60 d from August to February from 2011 to 2019. Animals were observed by trained technicians for winter growth (WG) and length (WL) scores from 1 to 5. A 1 for winter growth indicated no winter growth and a 5 indicated a full winter coat. For winter length, a 1 indicated short hair and a 5 indicated long. At scoring, a 5.08 cm by 10.16 cm hair sample was clipped directly behind the left shoulder below the top line and weighed. A thermal image was taken to determine average surface temperature of both the shaved (SHAVE) and unshaved (UNSHAVED) areas. Month of first winter growth (MFWG) was determined when the female reached an average winter growth score of 2.5 or higher. Calf performance was considered a trait of the dam and included AdjBW and d205wt. Phenotypic correlations were estimated on SHAVE, UNSHAVED, WG, WL, MFWG, hair weight, and month of first shedding (MFS), which was assessed during the spring of each year. Data were analyzed using the MIXED procedure of SAS with AdjBW and d205wt as response variables. The model included fixed effects of calf sex and MFWG with sire as a random effect. SHAVE was weakly positively associated with WG, WL (P < 0.05). There was no association between MFWG and MFS. MFWG was significant for AdjBW and d205wt with females starting winter growth in October having lighter calves at birth and weaning compared to those in December. Results suggest an association between MFWG and performance traits in Angus dams.
The objective of this study was to evaluate winter hair coat shedding ability in conjunction with apparent forage digestibility. Data were collected on fall calving purebred Angus females with calves from March until July in 2019 (n = 10) and 2020 (n = 31). Dams were observed once monthly by two trained technicians for winter hair coat shedding and were given a visual score of 1 to 5 with 1 indicating complete shed and 5 indicating no shed. Month of first shed (MFS) was determined when a female reached an average hair shedding score of 3.5 for any given month. Fecal samples were collected during the grazing months of March, May, and July for 5 consecutive days and were then analyzed via proximate analysis to calculate apparent digestibility of crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), ash, and dry matter percentage (DM) of forage. Data were analyzed using repeated measures of the MIXED procedure of SAS with a significance declared at P ≤ 0.05. The model included MFS, month, and MFS by month interaction with year and ambient temperature as a covariate with cow ID nested within MFS Interactions of MFS by month were observed for CP, ADF, NDF, ash, and DM. Females with a MFS in May or June showed decreased CP apparent digestibility during the month of May when compared with cows reaching a MFS in April or July (P = 0.04). For DM in July, females with an MFS in June and July were similar but decreased when compared to females with an MFS in April and May (P = 0.015). Interpretation of these results show no clear trend of an association between hair shedding ability and apparent digestibility. Further research into this area is important in understanding changes in overall cow performance due to adaptability.
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