Improvements in growth and carcass conformation through terminal sire crossbreeding systems may improve lamb value in a pasture-based system. Therefore, the aim of this study was to compare the effects of different terminal sires on parasitism, growth, composition, and marketability of grazing lambs. Suffolk (SU; n = 2) and Texel (TX; n = 2) sires were mated to commercial ewes at the WVU Organic Farm. April-born lambs were managed on pasture as one group until weaning in midJune, then were separated into 3 replicates per sire breed. Lambs were rotationally grazed for 93 d with paddock movement every 10 d. Lambs were supplemented at a rate of 2% of bodyweight with a 16% CP corn-soybean meal supplement. Weights were collected at weaning and then weekly for the duration of the study. Fecal egg counts (FEC) and FAMACHA scores were collected biweekly. Lambs were de-wormed when FAMACHA score was ≥ 3. Ultrasound measures of rib eye area (REA) were obtained at study conclusion and lambs were marketed at a graded auction. Sire breed did not impact weaning weight or growth rate throughout the test. Fecal egg count was slightly higher in TX vs. SU-sired lambs (257 vs 191 eggs/g; P < 0.05). FAMACHA scores were lower in TX vs. SU-sired lambs (1.58 vs. 1.96; P < 0.0001). Fewer deworming treatments were necessary in TX-sired lambs at 10% (4/39) whereas as SU-sired lambs required 55% (22/40) (P < 0.0001). TX-sired lambs had greater REA (11.57 vs 9.42 cm2; P < 0.0001) and graded better at the saleyard. Grading was set to a 6 pt scale with higher equating to higher sale price. Lambs sired by TX rams graded 5.2 and SU-sired lambs graded 3.6 (P < 0.0001). These data demonstrate that Texel-sired lambs required fewer dewormer treatments and were compositionally more desirable when marketed
Understanding the impact of genetic resistance to internal parasitism and infection status on feed efficiency could be valuable to selection and management programs. The aim of this study was to evaluate the effect of fecal egg count (FEC) estimated breeding value (EBV) and Haemonchus contortous (H.C.) infection on intake, feed:gain (F:G), and residual feed intake (RFI). Over two years, Katahdin lambs divergently selected for FEC EBV (LowFEC, n = 86; HighFEC, n = 87) were born mid-March at the Southwest Virginia Agricultural Research and Extension Center. Mid-July, lambs were transported to West Virginia University’s Animal Science Farm and fed using a Growsafe™. Lambs were provided a complete pellet (16% CP) ad libitum while individual intake was measured. Half of the lambs from each sire FEC EBV type were infected with 5,000 H.C. L3 larvae and observed for 6 weeks alongside uninfected contemporaries. Artificial H.C. infection resulted in lambs becoming moderately infected with FEC ranging from (0 – 1208 eggs/g). RFI was calculated as the difference between actual and expected intake. Expected intake was predicted based on average daily gain and metabolic body size. Intake was not affected by sire FEC EBV type or infection status (P > 0.10). Infection status did not affect F:G, however HighFEC lambs tended to have greater F:G values (13.5 vs. 6.8 kg feed:kg gain; P = 0.07). RFI was not affected by sire FEC EBV type or infection status (P > 0.10). Individual sire (n = 9) had a significant effect on intake and RFI (P < 0.05). Year and year x sire interaction did not have an effect on RFI or F:G (P > 0.40). Sire FEC EBV type and infection status did not impact feed efficiency. However, variation between sires independent of year indicates potential sire impact on progeny feed efficiency in sheep.
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