Residual feed intake, body composition, and fertility in yearling beef heifers12

Abstract

One hundred thirty-seven spring-born yearling beef heifers of British breed types were used to determine the relationships between residual feed intake (RFI) and growth rate, body composition, mature size, and fertility. Heifers were housed in a dry lot facility during the experimental period, and data were collected over a 2-yr period (yr 1, n = 67; yr 2, n = 70). Individual feed intake, BW, BCS, hip height, and ultrasonic measurements [subcutaneous rib fat (UBF), rump fat (URF), LM area (LMA), and intramuscular fat (IMF)] of body composition were recorded. Individual feed intakes (kg of TDN consumed/d) were used to calculate RFI combining both years of data. Heifers averaged 387.0 ± 19.4 d of age and 337.1 ± 29.9 kg of BW at initiation of the experiment. Mean ADG was 1.14 ± 0.21 kg/d during the trial. Based on RFI, with year of test and farm of origin included in the model as covariates, heifers were classified into groups: positive (POS; 0.74 kg of TDN/d) or negative (NEG; -0.73 kg TDN/d) for first analysis and high (HI), medium (MED), or low (LO; mean RFI = 1.06, -0.01, and -1.13 kg of TDN/d, respectively) subsequently. An initial phenotypic relationship (P < 0.05) between RFI and both UBF and URF (r = 0.19 and 0.17, respectively) was sustained (P < 0.01) with UBF (r = 0.27) and URF (r = 0.24) to trial conclusion. No other correlations with RFI were significant. Heifers classified as POS reached puberty earlier than those classified as NEG (414 ± 3.83 vs. 427 ± 4.67 d of age, P = 0.03), and possessed greater LMA per 100 kg of BW (LMACWT) at conclusion of the trial (P < 0.01). Medium heifers exhibited less URF (P < 0.05) compared with either HI or LO heifers at trial initiation. Low heifers possessed less LM area (cm(2)) per 100 kg of BW (P < 0.05) than HI but did not differ (P > 0.10) from MED heifers at either the beginning or the end of test. Additionally, a negative linear relationship was observed between RFI and age at puberty (P < 0.05). Each 1-unit increase in RFI corresponded to a decrease of 7.5 d in age at puberty, but did not affect pregnancy or conception rates (P > 0.10). Differences in body fat and rate of metabolism associated with RFI could delay reproductive maturity.

Grazed grass herbage intake and performance of beef heifers with predetermined phenotypic residual feed intake classification

“…The base RFI regression model (DMI explained by MLW and ADG) in this study accounted for 0.66 of the variation in DMI, which is comparable to other studies (Lancaster et al, 2008 and2009a;Shaffer et al, 2011) where high forage diets were fed (R 2 range from 0.53 to 0.64). These values are lower than those (0.71 to 0.77) obtained when RFI is determined on cattle fed high-energy diets (Basarab et al, 2003;Lancaster et al, 2009b;Kelly et al, 2010a).…”

“…Studies using low-energy roughage-based diets (Arthur et al, 2001b;Lancaster et al, 2009a;Shaffer et al, 2011) generally report larger s.d. of RFI (range of 0.71 to 0.97 v. 0.61 to 0.88) compared with those using high-energy grain-based diets (Nkrumah et al, 2007;Lancaster et al, 2008 and2009b).…”

Invited review: Improving feed efficiency in dairy production: challenges and possibilities

“…Because feed intakes and body condition scores did not differ during mid lactation between the divergent groups of lactating heifers, significant negative impacts of selection for reduced RFI during growth on fertility are not anticipated. Furthermore, research in growing beef heifers indicated that selection for reduced RFI should have no negative impacts on heifer or cow fertility, but may delay the time of sexual maturity (Basarab et al, 2011;Crowley et al, 2011;Shaffer et al, 2011). To date, no studies have evaluated RFI in dairy cows during the dry period or the relationship between RFI during growth or lactation and subsequent feed intake, BW or body condition during the dry period.…”

Genetic correlations between female fertility and postweaning growth and feed efficiency traits in multibreed beef cattle

“…Other studies have also found evidence of an unfavorable relationship between fertility and RFI. Shaffer et al (2011) classified RFI into two and three groups to study differences in fertility and found only age at puberty that was significantly different between positive and negative RFI groups with positive RFI associated with heifers becoming pubertal 13 d earlier, indicating selecting on RFI would delay heifer puberty. Arthur et al (2005) found that selection for low RFI would lead to a significant delay of five extra days for calving than selection for high RFI.…”