Brady Campbell, Program Coordinator, OSU Sheep Team
If you recall from last week, Jaborek et al. (2017) investigated how feed source and amount of feed offered per feeding affected lamb growth, performance, and carcass characteristics. In that experiment, lambs were fed to live weights of 130 – 140 lbs. and were fed for approximately for 100 days. This system is representative of the Eastern US sheep production. However, this system does not apply to all producers. For those producers that decide to retain lambs for an extended period of time beyond this typical market size and condition, lets try to understand how the number of days on feed affects lamb growth, performance, and carcass characteristics summarizing a paper by Jaborek et al. (2018) that fed lambs for an additional length of time (218 days on feed total).
For this experiment, a total of 48 Dorset x Hampshire crossbred lambs were fed one of three diets: 1) ad libitum access to a whole shelled corn based diet (WSC100), 2) a whole shelled corn based diet restricted to 85% of the ad libitum whole shelled corn based diet (WSC85), and 3) ad libitum access to an alfalfa pellet based diet (AP). As outlined in the previous experiment, main dietary ingredients were calculated on a per pound basis for whole shelled corn ($0.07/lb.), alfalfa ($0.27/lb.), and supplement ($0.23/lb.). Lambs were penned and fed by sex (ewes vs. wethers). Lambs were removed from the trial and harvested at an average age of 294 days or 218 days on feed.
From a performance standpoint, wether lambs had a greater average daily gain (ADG) when compared to ewe lambs (0.600 lbs./day vs. 0.551 lbs./day). In addition wether lambs had a greater dry matter intake (DMI) when compared to ewe lambs (4.25 lbs./day vs. 3.95 lbs./day).
When comparing diets, lambs offered WSC100 had the greatest final body weight (206 lbs.) when compared to WSC85 (183 lbs.) and AP (189 lbs.) fed lambs. Lambs offered WSC100 had a greater ADG (0.635 lbs./day) when compared to WSC85 (0.535 lbs./day) and AP (0.555 lbs./day) fed lambs. When comparing DMI, lambs fed WSC85 had the lowest DMI (3.05 lbs./day), whereas WSC100 fed lambs fell intermediate (3.59 lbs./day), and AP fed lambs had the greatest DMI (5.67 lbs./day). Gain to feed ratio remained similar among WSC fed lambs (0.1788 and 0.1760 lbs.), however both were greater when compared to AP fed lambs (0.0995 lbs.). From an economic perspective, feed cost per pound of gain remained similar between WSC fed lambs, where WSC100 ($2.97/lb.) and WSC85 ($3.25/lb.) lambs had a lower feed cost when compared to AP ($15.00/lb.) fed lambs.
From a carcass standpoint, wether lambs were heavier at harvest, which resulted in a heavier hot carcass weight (123 lbs.) when compared to ewe lambs (106 lbs.). Due to overall carcass fatness, wether lambs had a greater dressing percentage (64.97%) as compared to ewe lambs (60.94%). Interestingly, back fat was not significantly different between sexes (ewe – 0.55 in. vs. wether – 0.60 in.). However, boneless closely trimmed retail cuts (BCTRC) differed, with ewe lambs demonstrating a higher percentage (41.50%) as compared to wether lambs (39.35%).
In comparing diets, hot carcass weight differed among all three treatments; WSC100 fed lambs had the heaviest carcass weight (128 lbs.), with WSC85 lambs being intermediate (112 lbs.), and AP lambs having the lightest carcasses (103 lbs.). Dressing percentages were greater for both WSC diets (65.32% and 63.82%) when compared to the AP diet (59.72%). Body fat differed as lambs fed WSC100 had more back fat (0.69 in.) when compared to WSC85 (0.56 in.) and AP (0.48 in.) fed lambs. In addition, BCTRC was greatest for AP (41.99%) and WSC85 (41.045) fed lambs when compared to WSC100 (38.23%) fed lambs. However, loin muscle area, leg confirmation, and quality grade did not differ between diets.
As you may have noticed by now, there seems to be a trend in animal performance when offered specific feedstuffs. Jaborek et al. (2017, 2018) has demonstrated that offering lambs ad libitum WSC resulted in greater ADG and demonstrated the lowest feed cost per unit of gain. In both cases we have also been shown that this type of feeding system will result in the greatest amount of excess fat, which is undesired by both the packer and consumer. Unfortunately, at this time, most lambs are sold on a live weight basis, rather than a grid system like the beef industry. As a result, in order to receive the greatest premium for their lambs, many producers may continue to feed a diet in which results in the fastest route from point A to point B, even if this route results in the greatest amount of fat deposition. However, this feeding strategy may change based upon your end production goals (i.e. direct marketing of meat products). Regardless of which feeding strategy you choose, you now have a better understanding upon how diet, amount of feed offered, and time on feed can either negatively or positively affect your pocket book and final product.
Jaborek, J. R., H. N. Zerby, S. J. Moeller, and F. L. Fluharty. 2018. Effect of energy source and level, and sex on growth, performance, and carcass characteristics of long-fed lambs. Small Rumin. Res. 167: 61-69.