Heifer intake and feed efficiency as indicators of cow intake and efficiency

Abstract Text: Objectives were to determine the relationship between post-weaning feed efficiency and intake in heifers, and subsequent cow performance and reproduction as 2-yr-old cows. Post-weaning DMI, ADG, and backfat were evaluated on Angus and SimAngus heifers (n=511) over a 5-yr period. Heifers received similar forage-based diets, and individual DMI were recorded using the GrowSafe (Airdrie, AB) system. Residual feed intake (RFI) and residual BW gain (RG) were calculated. Heifers were classified into high, medium, or low RFI, RG, and DMI groups. Cow forage DMI, hip height, BW, BCS, and backfat via ultrasound were recorded at 60 d (lactating) and 240 d (dry) postpartum; 24-h milk production was estimated at 60 d. Cow predicted DMI was estimated by regressing DMI on metabolic BW, backfat, and 24-h milk production. Cow efficiency (cow_RFI) is the difference between actual and predicted DMI. The RFI classification did not affect (P≥0.12) reproductive traits; calf birth or weaning BW; cow BW, milk production, backfat, or BCS. Cows, classified with the most desirable heifer RFI, had reduced DMI (P<0.01) and most desirable cow_RFI (P<0.01) during lactation. Similarly, during the dry phase, cows within the low heifer RFI group tended (P=0.06) to eat less when compared to cows in the high heifer RFI group. The RG classification did not affect (P≥0.06) reproductive traits; calf birth or weaning BW; cow BW, hip height, BCS, milk production, backfat, cow_RFI, or DMI. Heifers, classified as low DMI, were less frequently (P<0.01) kept as replacements compared to medium and high DMI heifers, and were younger (P=0.04) at first calving compared to heifers classified as high DMI. Calves from cows, classified as high DMI heifers, had the greatest (P<0.01) birth BW; yet, there were no differences (P=0.47) in weaning BW. Intake classification had no effect (P≥0.24) on cow BCS, backfat, or milk production. Cows, classified as low DMI heifers, weighed the least (P=0.02) compared to cows from other heifer DMI groups. Cows, classified as high DMI heifers, had greater (P<0.01) hip heights than cows within the low DMI group, the medium DMI group was intermediate. Cows, classified as low DMI heifers, had reduced (P≤0.02) DMI and improved (P=0.04) cow_RFI compared to cows within the high heifer DMI group, the medium heifer DMI group was intermediate. This study suggests that selection for improvements in heifer RFI can result in reduced cow DMI without compromising production traits.

Keywords: beef cow, efficiency, intake, RFI