Location:2010 Annual Report
1a. Objectives (from AD-416)
Objective 1: Develop methods and strategies for measuring feed intake and related phenotypes of steers, replacement heifers, and mature cows. Objective 2: Determine breed and within-breed genetic effects on feed efficiency, growth, and fertility of cattle. Sub-objective 2.A. Determine breed and within-breed genetic effects on nutrient utilization. Sub-objective 2.B. Determine breed and within-breed genetic effects on reproductive efficiency. Objective 3: Discover QTL and estimate genomic effects for traits contributing to differences in efficiency among cattle. Objective 4: Fine map identified QTL for reproductive rate in cattle. Objective 5: Enhance existing simulation models to investigate genetic-by-environmental interactions on beef life-cycle efficiency and integrate into decision support software. Objective 6: Identify nutritional effects on expression of genes and subsequent phenotypes, and integrate this information with our current understanding of physiology to enhance management decisions.
1b. Approach (from AD-416)
Major challenges of the beef cattle industry are to improve efficiency and reduce negative environmental impacts of animal production. Provision of nutrients (feed) constitutes about 65 to 75% of the cost of beef cattle production. Less than 20% of the nutrients consumed are converted to useful products. The incomplete and inefficient utilization of nutrients has an adverse effect on efficiency of production and a negative effect on the environment. Traditional approaches have resulted in successful alteration of production traits such as weight at slaughter, growth rate, mature weight, and body composition, but have not altered feed efficiency. Those approaches do not provide the ability to economically identify animals with high genetic merit for feed efficiency on a timely basis, because the required phenotypic data are impractical to obtain in normal genetic evaluation programs. Available evidence suggests feed consumption and related traits are likely to be moderately heritable. These traits are extremely important components in any strategy for the permanent, cumulative, and sustainable genetic improvement of biological and economic efficiencies of beef production. Application of quantitative trait loci (QTL) technology provides opportunities to improve feed efficiency in beef production. The identification of QTL would make it possible to utilize the relatively large amount of observed variation and moderate heritability in improving feed efficiency. However, currently there are no tools (EPD, QTL, or markers for QTL) that facilitate direct selection to modify feed consumption, feed efficiency, or nutrient requirements in the growing-finishing animal or productive female. Research in this project is being undertaken to study genetic and environmental factors that lead to variation in efficiency in beef production. This project addresses measures of efficiency at different phases of the production system to identify those factors that have additive merit and antagonistic relationships across the different phases of production. The initial component of the project is to develop facilities and methodologies to efficiently collect economically and biologically important phenotypic data relevant to efficiency. After developing capabilities to measure the phenotypes, the contribution of genetics and environment/management to variation in efficiency of production will be determined. Genetic variation will be evaluated using both quantitative genetics and QTL discovery. Information gained from both the genetic and environmental studies will be used to parameterize simulation models that provide decision support software to allow producers to simulate potential outcomes to optimize production efficiency when different combinations of animal genetics and management strategies are used.
3. Progress Report
Phenotypic data for individual feed intake and weight change were collected on steers (n = ~ 420), heifers (n = ~ 400), and mature cows (n = ~ 180). Association analyses for growth and feed intake in previously characterized steers and genotypes from the Bovine SNP50 Chip were conducted. Two genomic regions for feed intake were identified and fine mapping of those regions has occurred. Phenotypic measures of milk production, mammary gland soundness, and feet and leg structural quality were collected on two-year-old cows (n = ~ 250). Reproductive success and calf performance were determined. Reproductive tracts were collected from 37 repeat-breeders and 34 contemporary herd mates. Repeat breeders had smaller ovaries with fewer follicles. Gene expression analysis was performed on ovarian cells from High and Low fertility cows for anti-Müllerian Hormone (AMH) and Pentraxin 3 (PTX3). Anti-Müllerian-Hormone gene expression was decreased in the ovaries of Low fertility cows. There was no difference in PTX3 gene expression between the Low and High fertility cows. Ovarian follicle counts of 14-month-old heifers (n = 450) were performed by ultrasonography, and subjected to association analysis using genotypes from the Bovine SNP50 Chip. A region on chromosome 2 and one on chromosome 3 were identified to be associated with antral follicle count. Nutritional treatments were imposed on 174 heifers to determine the effects of peripuberal over nutrition on subsequent feed and production efficiency. Reproductive data was collected on 194 females that had received nutritional treatments in the previous years. Feed intake (n = 59) and nutrient balance trials were conducted on 2-year-old cows that had previously been developed as heifers. Nutritional treatments were imposed on 120 heifers to determine the effects of under nutrition. Ovarian size and antral folicle counts were determined. Nutritional treatments were applied to ~200 cows to determine the effect of uterine nutrient environment on the subsequent production efficiency of daughters and the carcass quality on sons. Growth, puberty, and pregnancy data was collected on ~200 daughters that were the result of the previous year’s uterine nutrient environment study. Component traits that impact efficiency of feed utilization were estimated for 1,212 steers that had measured records of individual daily feed intake. These component traits were efficiency of protein accretion and maintenance requirements and they were estimated using the DECI model. Feed conversion ratio and residual feed intake were obtained for each steer from the measured data on individual feed intake and weight gain. Phenotypic correlations were estimated between these measures of feed efficiency and the DECI model predicted component traits.
1. A method for comparing feed efficiency across groups of cattle. Approaches currently used to identify efficient cattle allow for cattle to be ranked within study or experiment; however, these approaches do not lend themselves to comparing the feed efficiency of cattle across populations. The inability to compare efficiency measurements across studies reduces the ability to identify superior animals for genetic selection, and makes identifying common physiological differences that result in improved feed efficiency difficult. Research conducted at the US Meat Animal Research Center, Clay Center, NE, demonstrated that using robust biological systems models such as the Decision Evaluator for the Cattle Industry model developed by ARS provides a method to compare data across studies and provides more accurate estimates of feed efficiency in small data sets.
2. Providing glucose to the small intestine does not decrease amino acid metabolism. Improving the efficiency that nitrogen is converted to animal products improves feed efficiency and decreases nutrient release into the environment. Catabolism of amino acids at the small intestine represents one of the major events in the metabolism of protein that leads to inefficiency. Research conducted at the US Meat Animal Research Center, Clay Center, NE, reported that providing glucose, a readily available energy source, to the small intestine did not improve the net appearance of amino acids into circulation. These finds suggest that amino acid catabolism by the small intestine is not solely driven by energy metabolism, and occurs to support other metabolic requirements.
3. Blood progesterone concentration decreases as the cow ages. Replacing cows that are no longer reproductively sound is one of the major costs that effect production efficiency. In cattle, progesterone is required to maintain pregnancy. Research conducted at the US Meat Animal Research Center, Clay Center, NE, reported that blood progesterone levels decreases as the cow ages. The decrease in blood progesterone occurred both at breeding as well as during pregnancy. These findings indentify one biological mechanism that can cause a decrease in fertility as the cow ages.
Echternkamp, S.E., Cushman, R.A., Allan, M.F. 2009. Size of Ovulatory Follicles in Cattle Expressing Multiple Ovulations Naturally and Its Influence on Corpus Luteum Development and Fertility. Journal of Animal Science. 87(11):3556-3568.