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Feed efficiency is associated with reproductive performance in dairy cows
For residual feed intake (RFI) to be used as an alternative measure of feed efficiency in the dairy industry it must not be unfavorably correlated with fertility. Previous research in beef cattle, sheep and pigs suggests that reproduction is impacted by RFI status. Therefore, the objective of this study was to determine the phenotypic relationship between RFI and reproductive performance in dairy cows. Feed, milk, and health data were collected on 1,513 Holstein cows in various stages of production at Virginia Tech and Iowa State University for 84 d. Daily measurements of DMI, milk yield, weekly milk composition, and monthly body weight were used to calculate RFI. Cows with lower RFI were identified as more feed efficient. Four measures of reproductive performance were examined: number of services (NS; n = 1,037), previous days dry (DD; n = 760), days open (DO; n = 716), and days to first calving (DFC; n = 472). Correlation and ANOVA analyses with ad hoc comparisons using a Tukey adjustment were performed in R. For the ANOVA, cows were categorized into top 5% (High RFI; n = 50), middle 5% (Medium RFI; n = 50), and bottom 5% (Low RFI; n = 50). Correlations were calculated between reproductive measures and RFI. There was a weak positive phenotypic correlation (rp = 0.18 ± 0.04, P < 0.01) between NS and DO with RFI suggesting that feed efficient cows may require fewer services to become pregnant and shorter periods to become bred. There was also a weak negative phenotypic correlation (rp = -0.14 ± 0.04, P < 0.01) between DFC and RFI suggesting increased days for feed efficient cows to produce their first calf. Medium RFI cows had greater DD (P = 0.046; 109.5 ± 13.9) compared to High RFI cows (63.3 ± 11.7), but neither differed (P ≥ 0.12) from Low RFI cows. High RFI cows had increased NS (P= 0.016; 4.80 ± 0.54 services) compared to Low RFI cows (3.05 ± 0.33 services), but neither differed (P ≥ 0.14) from Medium RFI cows. Low RFI cows had lower DO (P ≤ 0.05; 83.61 ± 10.4 d) than both Medium (126.0 ± 14.3 d) and High RFI cows (115.9 ± 10.4 d). Therefore, feed efficient cows had decreased NS and DO. Overall, results suggested that selection for RFI will not unfavorably impact reproduction in dairy cows.
Keywords: feed efficiency, reproductive performance, residual feed intake