Effect of energy source and level, and sex on growth, performance, and carcass characteristics of long-fed lambs

The objective of the present study was to assess energy source, level, and sex of the lamb, on the growth, performance, and carcass characteristics of long-fed lambs (218 days on feed and 294 days of age). Ewe (n = 24) and wether (n = 24) lambs were blocked by sex and stratified by initial weight to pens containing four lambs within a pen, with two pens of each sex assigned to each of the three dietary treatments. The three diets offered were ad libitum access (WSC100) to whole shelled corn (WSC), 85% access of the ad libitum WSC diet (WSC85), and ad libitum access to alfalfa pellets (AP). Lambs offered WSC100 had greater (P <  0.05) ADG when compared with lambs offered WSC85 or AP, which resulted in a greater (P <  0.05) final body weight (93.6, 83.4, 86.0 kg, respectively). Lambs offered AP had a greater (P <  0.01) DMI when compared with lambs offered WSC100 or WSC85. Wether lambs had a greater final body weight (90.6 vs. 87.5 kg; P <  0.05), ADG (P <  0.05), and DMI (P <  0.01) when compared with ewe lambs. Lambs offered WSC had a greater (P <  0.01) G:F and a lower (P <  0.01) feed cost per unit of gain when compared with lambs offered AP. Lambs offered WSC100 had a greater final body weight (P <  0.05), hot carcass weight (HCW; P <  0.05) and visceral fat weight (P <  0.01) compared with lambs offered AP or WSC85. Lambs consuming WSC100 or WSC85 had a lighter reticulum (P <  0.01), omasum (P <  0.01), small (P <  0.01) and large intestine (P <  0.05), cecum (P <  0.05), and total tract weight (P <  0.01), but a greater (P <  0.05) amount of kidney fat compared with lambs offered AP. Wether lambs had a greater (P <  0.05) HCW, but a lighter (P <  0.05) small intestine weight when compared with ewe lambs. Lambs offered WSC100 had a greater final body weight (P <  0.01) and produced carcasses with a greater HCW (P <  0.01), backfat thickness (P <  0.05), body wall thickness (P <  0.01), yield grade (P <  0.05), and marbling score (P <  0.05) when compared with carcasses from lambs offered AP or WSC85. However, carcasses from lambs offered WSC100 had a lower percentage of boneless closely trimmed retail cuts (P <  0.05) when compared with carcasses from lambs offered AP or WSC85. Both WSC100 and WSC85 diets produced lamb carcasses with greater (P <  0.01) dressing percentages and kidney fat weights when compared with carcasses from lambs offered AP. Wether lamb carcasses had a greater final body weight, HCW, dressing percentage, and BWT when compared with ewe lamb carcasses. Overall, lambs offered WSC100 or WSC85 grew faster and more efficiently with a lower feed cost of gain. Lambs offered WSC100 and WSC85 also had a lower total digestive tract weight compared with lambs offered AP. However, feeding WSC100 produced carcasses with greater amounts of fat in multiple fat depots when compared with lambs offered AP or WSC85.