1a.Objectives (from AD-416):
The objective of this cooperative research project is to determine the effects of energy supplementation of Angus cows during the third trimester of pregnancy on intramuscular fat development in their calves fed for 50, 75, or 100 days during the finishing period and to evaluate the genomics of fatty acid deposition in the milk of the dam and in the calves.
1b.Approach (from AD-416):
Purebred Angus cows (n=100) will be used in this study. Cows will be bred natural service in late spring 2011-2013 to Angus bulls (n=8 per year) to spring calve for three calving seasons. Heifers will be managed on native range or improved pasture throughout the year, and 50% will be fed additional feed during the last trimester of pregnancy. Preweaning management will be on native range or improved pasture, and calves will be weaned at approximately 7 mo. of age. Calves will be grazed on wheat pasture during the fall and winter and warm-season grasses in the summer until the end of the grazing season. Steer calves will be divided into three groups, and 1/3 will be fed for 100 days and then shipped for harvest, 1/3 will be fed for 75 days and shipped for harvest, and the remaining will be fed for 50 days and shipped for harvest. Prior to shipping for harvest, calves will be bled to collect DNA. Calves will be processed and carcass data collected, including marbling score and carcass quality grade. The wholesale rib will be collected and fatty acid composition determined from the longissimus dorsi. Relationships between polymorphisms in the leptin gene and other genes related to fat deposition and various fatty acids in the milk of the dam and intramuscular fat of the calf will be determined.
Location cow herds were divided into the two winter nutrition treatments with six groups per treatment (each group approx. 25 cows). Cows in the high energy treatment received 5 lbs 20% protein supplement (approx. 80% TDN) and cows on the low energy treatment received 2.5 lbs 40% protein supplement (approx. 80% TDN) starting 60 days prior to calving. The groups have grazed native pastures or other warm-season perennials during the forage growing season. The region has experienced a second year of extreme drought and hot weather during the summer. The calves will be weaned in October, and developed in a normal growing-finishing phase before harvesting. The second rep will be conducted during the following year.