Date of Graduation
Davis College of Agriculture, Natural Resources and Design
Animal and Nutritional Sciences
Eugene E. D. Felton.
One hundred thirty-seven spring born yearling beef heifers of English 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 drylot facility during the trial and data were collected over a two-year period (year 1, n=67; year 2, n=70). Individual feed intake, body weight (BW), body condition score (BCS ), hip height (HH), and carcass ultrasound measurements (subcutaneous rib and rump fat; RIF and RUF, respectively, longissimus muscle area; LMA, and intramuscular fat; IMF ) were collected. Individual feed intakes were expressed as kg of TDN consumed per day and were used to calculate RFI combining both years' data. Heifers averaged 387.0 +/- 19.4 days of age (DOA) and 337.1 +/- 29.9 kg BW at trial initiation. Mean average daily gain (ADG) was 1.14 +/- 0.21 kg/d. A slight relationship (P < 0.05) existed between RFI and both RIF and RUF (r = 0.19 and 0.17, respectively) initially and was increased (r = 0.27 and r = 0.24, respectively; P < 0.01) at trial conclusion. Heifers were classified into groups (POS; mean RFI=0.74 vs. NEG; -0.73 and HIGH; mean RFI=1.06, MEDIUM; -0.01, and LOW; -1.13) based on RFI (kg TDN/d), with year of test and farm of origin included in the model as covariates. POS heifers tended to possess more RIF (P = 0.051) and ribeye area (cm2) per hundred kg of BW (LMACWT) (P = 0.078) than NEG heifers at trial initiation, while LMACWT was greater in POS heifers at trial conclusion (P < 0.01). POSITIVE heifers reached puberty earlier than NEG heifers (414 vs. 427 day, respectively, P = 0.03). MEDIUM heifers exhibited less RIF and RUF (P < 0.05) when compared to either HIGH or LOW at trial initiation. LMACWT was less (P 0.10) from MEDIUM females at both beginning and end of test. A negative linear relationship existed between RFI and AGE at PUBERTY (P < 0.05). Each one unit increase in RFI corresponded to a reduction of 7.54 days in AGE at PUBERTY; however, no differences existed between groups in pregnancy or conception rate. Given that RFI was significantly correlated with subcutaneous fat measures and the known relationship between fatness and reproductive maturity, further investigation is warranted.
Shaffer, Kevin S., "Residual feed intake, body composition and fertility in yearling beef heifers" (2010). Graduate Theses, Dissertations, and Problem Reports. 2975.