The effects of genotype-by-environment interactions on body condition score across three winter supplemental feed environments in a composite beef cattle breed in Montana

Authors: Ling, Ashley; Hay, El Hamidi

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/28/2024
Publication Date: 2/29/2024
Citation: Ling, A.S., Hay, E.A. 2024. The effects of genotype-by-environment interactions on body condition score across three winter supplemental feed environments in a composite beef cattle breed in Montana. Journal of Animal Science. 8. Article txae024. https://doi.org/10.1093/tas/txae024.
DOI: https://doi.org/10.1093/tas/txae024

Interpretive Summary: Body condition scores (BCS) are commonly collected in cattle management as a tool for assessing animal nutrition and health. Body condition fluctuates with season and production and its measure at calving and breeding has been shown to be associated with health and fertility traits that impact profitability of calf-cow operations. In the Northern Great Plains region of the United States cattle endure harsh winters and producers must provide nutritional supplementation in order for spring-calving cows to sustain a body condition adequate for producing healthy calves and maintaining high fertility. BCS are known to have a low-to-moderate genetic basis and some individuals may have better potential to weather extreme cold weather conditions with fewer resources. The present study evaluates the potential of genotype-by-environment interactions between BCS measured at calving and breeding and three winter supplementation treatments differing in crude protein content and range access. Data was collected from a USDA research herd of composite beef cattle maintained in Montana in a calf-cow operation system. Genetic correlations between environments differing in crude protein content were as low as 0.65 and 0.78, providing tentative evidence of genotype-by-environment interactions for BCS measured at calving across a protein gradient.

Technical Abstract: Cattle operations in the Northern Great Plains region of the United States face extreme cold weather conditions and require nutritional supplementation over the winter season in order for animals to maintain body condition. In cow-calf operations, body conditions scores (BCS) measured at calving and breeding have been shown to be associated with several economically-important health and fertility traits and so maintenance of BCS is both an animal welfare and economic concern. BCS measured at various production stages has a low-to-medium heritability, indicating a large environmental influence but sufficiently large genetic basis for selection. The present study evaluated BCS measured prior to calving (late winter) and breeding (late summer) under three winter supplementation environments in a multi-trait linear mixed model. Traits were discretized by winter supplementation and genetic correlations between environments considered a reflection of evidence for genotype-by-environment interactions between BCS and diet. Winter supplementation treatments were fed from October through April and varied by range access and protein content: 1) feedlot environment with approximately 15% crude protein (CP) corn/silage diet, 2) native range access with 1.8 kg of an 18% CP pellet supplement, and 3) native range access with a self-fed 50% CP mineral supplement. A total of 2,988 and 2,353 records were collected on 1,010 and 800 individuals for pre-breeding and pre-calving BCS, respectively. Heifers and cows came from a composite breed of beef cattle developed and maintained by the USDA Fort Keogh Livestock and Range Research Laboratory near Miles City, Montana. Genetic correlations between Treatments 1 and 2, 1 and 3, and 2 and 3 were 0.98, 0.78, and 0.65 and 1.00, 0.98, and 0.99 for pre-calving and pre-breeding BCS, respectively. This provides moderate evidence of genotype-by-environment interactions for pre-calving BCS under Treatment 3 relative to Treatments 1 and 2, but no evidence for genotype-by-environment interactions for pre-breeding BCS. Treatment 3 differed substantially in CP content relative to Treatments 1 and 2, indicating that some animals differ in their ability to maintain BCS up to spring calving across a protein gradient. These results indicate the potential for selection of animals with increased resilience under cold weather conditions and high protein, restricted energy diets to maintain BCS.