In sheep farms, achieving economic and productive efficiency and sustainability goals is directly related with the reproductive management of the animals. Genetically, the male contribution to the offspring is 50%, but in practical terms, there is a greater potential impact of the ram on reproductive results, because one male has the potential to affect a large group of females and therefore greatly affects the entire flock. Unfortunately, the selection of males for breeding in the US sheep industry has been traditionally conducted based on phenotypical traits, without a genetic/reproductive evaluation, and/or health assessment or records. Therefore, it is important to establish integrative management practices to select the rams and ram lambs to be used in the breeding season. Among these practices are genomic testing, a comprehensive breeding soundness evaluation and assessment of health status and records of the males before the breeding season, to detect and correct potential issues.

Vitamin A and its metabolite, retinoic acid (RA), are important regulators of cell differentiation and organ morphogenesis. Its impact on beef cattle muscle growth remains undefined. Angus steer calves were administrated with 0 (control) or 150,000 IU vitamin A (retinyl palmitate in glycerol, i.m.) per calf at birth and 1 month of age. At 2 months of age, a biopsy of the Biceps femoris muscle was obtained to analyze the immediate effects of vitamin A injection on myogenic capacity of muscle cells. The resulting steers were harvested at 14 months of age. Vitamin A administration increased cattle growth at 2 months. At 2 months of age, Vitamin A increased PAX7 positive satellite cells and the expression of myogenic marker genes including PAX7, MYF5, MYOD and MYOG. Muscle derived mononuclear cells were further isolated and induced myogenesis in vitro. More myotubes and a higher degree of myogenesis was observed in vitamin A groups. Consistently, vitamin A increased Latissimus dorsi (LD) muscle fiber size at harvest. In addition, vitamin A increased the ratio of oxidative type I and type IIA fibers and reduced the glycolic type IIX fibers. Furthermore, we found that RA, a key bioactive metabolite of vitamin A, activated PPARGC1A promoter, which explains the upregulated expression of PPARGC1A in skeletal muscle. Vitamin A administration to neonatal calves enhanced postnatal muscle growth by promoting myogenesis and increasing satellite cell density, accompanied with a shift to oxidative muscle fibers.

The aim of this study was to assess the seasonal effect of an embryo transfer program in the tropics on the donor response, recipient reproductive performance and calf growth from birth to weaning. This study included five-year records from 145 donors, 1149 embryo transfers (ET) and 609 in calves. The effect of the season (dry or wet) was evaluated at the time of embryo flushing, embryo transfer and birth of the calves. There was a seasonal effect on the yield and quality of the embryos. The number of nonfertilized and transferable good quality embryos increased in the wet season. For the recipients, the probability of pregnancy after an ET decreased by 6% for each year of the dam’s age. However, no seasonal effect was found when comparing ET calves with their control group (natural mating—NM), nevertheless, weaning weight was associated with birth body weight, treatment, sex of the calf, season at birth, year of treatment, and dam’s age. Calves born by NM had lower average daily gain (ADG), and male calves registered higher gains than females. Likewise, calves born during the rainy season had lower ADG compared with calves born during the dry season. In conclusion, this study shows that seasonal effect is more apparent in donor and calf performance than in the recipients.

The objective of this experiment was to characterize relative expression of mRNA related to genes involved in Cu absorption in the duodenum of different breeds of sheep. Opportunistic liver and small intestine samples were collected from three harvested market weight Lincoln and Suffolk wether lambs (3 to 4 months of age) fed a low-quality forage based diet. A 5 cm sample of the duodenum (15 cm aboral from the pyloric sphincter) was collected from each lamb at the time of slaughter. Samples were immediately excised, sliced open, and washed with a PBS solution. The mucosal lining of the intestine was scraped with a scalpel blade to collect enterocytes. The scraped enterocytes were placed into a conical tube containing RNAlater. Furthermore, a one cm cubed sample from the center of the right lobe of the liver was collected from each lamb, washed with PBS solution, and stored in a conical tube until liver Cu concentrations could be determined. All intestinal and liver samples were stored at 4°C until transported back to the laboratory. Total enterocyte RNA was extracted and purified using TRI reagent and RNeasy. Primers for antioxidant 1 (ATOX1), Cu transporting alpha-polypeptide Atpase (ATP7A), Cu transporting beta-polypeptide Atpase (ATP7B), and Cu transporter1 (CTR1), were designed for real time PCR analysis. Liver Cu concentrations were decreased (P < 0.05) in Lincoln (225.3 ± 23.1 mg Cu/kg DM) compared with Suffolk lambs (342.1 ± 31.2 mg Cu/kg DM). The relative mRNA expression of ATOX1 (P < 0.05), ATP7B (P < 0.01), and CTR1 (P < 0.04) in duodenal enterocytes were decreased in Lincoln compared with Suffolk lambs. These data indicate that Cu absorption from the duodenum may be different in these breeds of sheep. Further research examining the impact of dietary Cu dose on genes involved in Cu absorption in different breeds of sheep as well as identification and quantification of proteins involved in Cu absorption, is warranted.