INTERACTION OF MILK, FAT AND PROTEIN YIELD GENOTYPE WITH FEEDING LEVEL AND INDICATORS OF COW COMFORT

Open Access
Author:
Dekleva, Matthew William
Graduate Program:
Animal Science
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
May 13, 2010
Committee Members:
  • Chad Daniel Dechow, Thesis Advisor
Keywords:
  • production
  • environment
  • genotype
Abstract:
The objective of this study was to determine the effect of nutritional management and cow comfort indicators on the level of genetic expression for production traits. There were 305 d milk, fat and protein yields available for 970 cows from 11 tie-stall herds in Pennsylvania. All herds were visited monthly for a period of 6 months to measure individual cow feed intake, BCS and BW. Feed samples were collected on each visit and analyzed for dry matter percentage, crude protein (CP) percentage and calculated net energy of lactation (NEL). Sire predicted transmitting ability (PTA) was available for all 970 cows, while 881 cows were genotyped and received an Igenity Score (IS) for milk, fat, and protein yield. Two-trait animal models and regression of yield on sire PTA for milk, fat and protein production were used to detect the presence of genotype by environment (GxE) interactions. Environments were defined according to feeding levels of dry matter, dietary composition, and cow comfort measures taken from the facilities. These included stall size (SS), hock lesion score (HLS) and udder hygiene score (HygS) to measure stall management. Response to selection was lower in environments where levels of feed refusals, percentage of CP, and calculated NEL concentration in the ration were low when compared to environments that fed at high levels for these variables. Animal models showed that large animals are more affected by low levels of feeding of dry matter, CP percentage, NEL concentration, and high HLS.