. 2007. Relationships between progeny residual feed intake and dam productivity traits. Can. J. Anim. Sci. 87: 489-502. Two hundred and twenty-two yearling calves and their dams were used to examine the phenotypic (r p ) relationships between progeny residual feed intake (RFI) and maternal productivity across 10 production cycles. Progeny RFI ranged from -3.95 to +2.72 kg as fed d -1 (SD = 0.94), while RFI adjusted for off-test backfat thickness (RFI adj ), ranged from -2.48 to +1.53 kg as fed d -1 (SD = 0.88). Progeny RFI and RFI adj were unrelated to on-test age, body weight, growth rate, and ultrasound longissimus thoracis area and positively related to feed intake (r p = 0.51 to 0.53; P < 0.001), feed to gain ratio (r p = 0.44 to 0.46; P < 0.001), feeding behaviour traits (r p = 0.29 to 0.36; P < 0.001) and cow RFI (r p = 0.30, P < 0.05). Progeny RFI was positively related to measures of body fat (r p = 0.21 to 0.27; P < 0.05), but these relationships disappeared when RFI was adjusted for off-test backfat thickness. Cows that had produced LOW (≤ 0.5 SD), MEDIUM (± 0.5 SD) or HIGH (≥ 0.5 SD) RFI adj progeny were similar in pregnancy (95.6 vs. 95.3 vs. 96.0%, P = 0.90), calving (84.9 vs. 83.4 vs. 86.3%, P = 0.62) and weaning (81.5 vs. 80.2 vs. 82.3%, P = 0.79) rates. However, cows that produced HIGH RFI adj progeny had a higher twinning rate (3.77 vs. 0.35 vs. 0.00%, P < 0.001) and an increased calf death loss (8.06 vs. 4.24 vs. 4.02%, P = 0.10) compared with cows that produced MEDIUM or LOW RFI adj progeny. Cow body weight over 10 production cycles was similar at weaning, pre-calving and pre-breeding for dams that had produced LOW, MEDIUM and HIGH RFI adj progeny, and dams that produced LOW RFI adj progeny consistently averaged 2-3 mm more back fat thickness than dams that produced HIGH RFI adj progeny. Calf birth weight, pre-weaning ADG and 200-d weight, and cow production efficiency and calving interval were similar among dams that produced LOW, MEDIUM and HIGH RFI adj progeny. In addition, dams that produced LOW RFI adj progeny consumed less feed during their second trimester of pregnancy (10.9 vs. 11.6 vs. 12.2 kg DM d -1 , P < 0.05), had lower RFI values (-0.05 vs. 0.44 vs. 1.88 kg as fed d -1 , P = 0.018) and calved later in the year (96 vs. 90 vs. 91 d Julian, P < 0.001) than dams that produced MEDI-UM and HIGH RFI adj progeny. These results showed that efficient RFI progeny and dams consumed less feed, had improved feed to gain ratio and spent less time in feed activity than inefficient cows and calves. In addition, cows that produced efficient calves were fatter, had fewer twins, less calf death loss and produced the same weight of calf weaned per cow exposed to breeding compared with cows that produced inefficient progeny. However, cows that produced efficient or low RFI progeny calved 5-6 d later in the year than cows that produced inefficient or high RFI progeny, indicating a need to monitor reproductive fitness in low RFI replacement heifers and breeding bulls. . La RFI et la RFI adj de la progén...

Basarab, J. A., Colazo, M. G., Ambrose, D. J., Novak, S., McCartney, D. and Baron, V. S. 2011. Residual feed intake adjusted for backfat thickness and feeding frequency is independent of fertility in beef heifers. Can. J. Anim. Sci. 91: 573–584. This study examined the effects of residual feed intake (RFI), RFI adjusted for off-test backfat thickness (RFIfat) and RFI adjusted for off-test backfat thickness and feeding event frequency (RFIfat & activity) on heifer fertility and productivity. Beef heifers (n=190) were monitored for individual daily feed intake and feeding event activity over 108–112 d using the GrowSafe System® and assessed for age at puberty based on plasma progesterone concentration. Individual animal daily feed intake, feeding event activity and off-test backfat thickness were then used to calculate RFI, RFIfat and RFIfat & activity and group heifers as either negative ([−], RFI<0.0) or positive ([+], RFI≥0.0) for RFI. Heifers averaged 298 kg (SD=34) in body weight, were 276 days of age (SD=19) at the start of test, grew at 0.90 kg d−1 (SD=0.21), consumed 7.62 kg DM head−1 d−1 (SD=0.84) and had a feed conversion ratio of 8.93 (SD=2.43). Age (351 d, SD=43) and weight (367.3 kg, SD=45.0) at puberty were similar between [−] and [+] RFI heifers, but age at puberty was delayed in [−] RFIfat (P=0.04) and RFIfat & activity (P=0.08) heifers compared with [+] RFIfat and RFIfat & activity heifers. Efficient or [−] RFI heifer exhibited a lower pregnancy (76.84 vs. 86.32%, P=0.09) and calving rate (72.63 vs. 84.21%, P=0.05) compared with [+] RFI heifers. These differences were partially removed in [−] RFIfat and completely removed in [−] RFIfat & activity compared with their [+] RFI counterparts (pregnancy rate, 80.85 vs. 82.29%, P=0.80; calving rate, 75.53 vs. 81.25%, P=0.34). No differences were observed between efficient and inefficient heifers in calving difficulty, average calving date, age at first calving, calf birth weight, calf pre-weaning ADG, calf weaning weight and heifer productivity. However, [+] RFI heifers exhibited a 1.9-fold higher calf death loss compared with [−] RFI heifers (11.11% vs. 5.71%, P=0.24). This difference was more pronounced in [+] RFIfat and [+] RFIfat & activity heifers, which exhibited 2.2-fold (11.84% vs. 5.33%, P=0.15) and 3.0-fold (12.66% vs. 4.17%, P=0.06) higher calf death loss compared with [−] RFI heifers. There was no relationship of RFI adjusted for backfat thickness and feeding activity on fertility traits indicating that backfat thickness and feeding activity may be associated with feed intake and should be considered when selecting heifers for improved feed efficiency.

Canadian beef consumption is approximately 31 kg per annum, or a third of all meats consumed. Beef is a nutrient-rich food, providing good quality protein, vitamins B-6 and B-12, niacin, iron, and zinc. However, animal fats have gained the reputation of being less healthy. The identification of the anticarcinogenic effects of beef extracts due to the presence of conjugated linoleic acid (CLA) has heightened interest in increasing the amount of CLA deposited in beef. Beef cattle produce CLA and deposit these compounds in the meat; thus, beef consumers can receive bioformed CLA. Beef contains both of the bioactive CLA isomers, namely, cis-9, trans-11 and trans-10, cis-12. The relative content of these CLA isomers in beef depends on the feeds consumed by the animals during production. Feeding cattle linoleic acid-rich oils for extended periods of time increases the CLA content of beef. Depending on the type and relative maturity of the pasture, beef from pasture-fed cattle may have a higher CLA content than beef from grain- or silage-fed cattle. In feedlot animals fed high-grain diets, inclusion of dietary oil along with hay during both the growth and finishing phases led to an increase in CLA content from 2.8 to 14 mg/g beef fat, which would provide 77 mg CLA in an 85-g serving of beef. The CLAs appear to be concentrated in intramuscular and subcutaneous fat of beef cattle, with the CLA trans-10, cis-12 isomer being greater in the subcutaneous fat.