Can Restricting Feed Intake Benefit your Lamb Feeding Program?

Brady Campbell, Program Coordinator, OSU Sheep Team

With lambing season upon us, many are concentrated on getting lambs on the ground and getting them off to a good start. Although this is an extremely important step in the continual management of your flock, we must also be thinking one-step ahead. By this I mean, what will be your feeding strategy after your lambs are weaned a few months from now. Some producers may decide to sell their lambs as feeders directly after weaning, but for those that decide to retain their lambs and feed them out, how will your lambs be fed? What will your diet be composed of and will you be providing the diet at ad-libitum or at a restricted intake? Thinking about this, have you ever considered how the feeding strategy you choose could affect the feed efficiency and performance of your growing lambs? If you haven’t, no worries. Thankfully, Murphy and others (1994) did just this to determine the effects of feeding high concentrate diets, at restricted intakes, on the digestibility and metabolism in growing lambs.

In order to determine these effects, the authors studied lambs in two different trials. Each trial used 12 wether lambs each. Trial 1 was conducted in order to determine the effects of restricting intake of diets increasing in percentage of concentrates. The dietary treatments used in trial 1 were 1) 22% concentrate diet fed for ad-libitum intake, 2) 39% concentrate diet fed at 90% ad-libitum intake, 3) 61% concentrate diet fed at 80% ad-libitum intake, and 4) 90% concentrated diet fed at 70% ad-libitum intake. Restrict fed diets were based upon the intake of lambs fed dietary treatment 1. Dietary concentrate consisted of ground corn and soybean meal, with the remainder of the diet consisting of ground corncobs as a fiber source (Table 1).

Upon the completion of trial 1, trail 2 was conducted in order to determine the effects of feedings diets containing the same amount of concentrate at restricted levels. In trial 2, high concentrate diets were fed at 1) ad-libitum intake, 2) 90% of ad-libitum intake, 3) 80% of ad-libitum intake, and 4) 70% of ad-libitum intake. Restricted intakes were determined using the same format as shown in trial 1. However, in trial 2, 92% of the diet consisted of ground corn and soybean meal, whereas corncobs made up only 8% of this diet (Table 2).

In trial 1, results showed that lambs fed restricted intake diets with increasing percentages of concentrate linearly improved dry matter, organic matter, acid detergent fiber, and neutral detergent fiber digestibility’s (Table 3). Therefore, as the percentage of concentrate in the diet and dietary restriction increases, lambs demonstrated an overall greater digestibility of the feed offered. However, it should be noted that starch digestibility was not affected by the feeding strategy used. Due to the design of the diets in trial 1, metabolizable energy of the diet increased as the percentage of concentrate increased. Thus, lambs consuming restrict fed, high concentrate diets were at an advantage as they may have had access to more energy used for tissue growth.

In trial 2, results illustrated that restrict feeding led to a linear improvement of dry matter, organic matter, acid detergent fiber, crude protein, and starch digestibility. As outlined by Murphy and others (1994) and supported by Tyrrell and Moe (1975), improvement in digestibility may have been the result of slower passage rates due to less feed being within the digestive system. In addition, digestibility of dietary protein may have also been effected by protein source. Due to the design of the diets in trial 2 (Table 2), in order to maintain consistent chemical composition and metabolizable energy values, as intake restriction increased, the inclusion of soybean meal increased as it substituted corn. Therefore, due to soybean meal having a greater true digestibility as compared to corn, lambs receiving restrict fed diets may perform to a greater degree as compared to the ad-libitum fed counterparts.

As shown in these two trials, restricting feed intake can lead to a greater energy intake due to an increase in diet digestibility. Restricting feed intake also allows for a greater retention time for feedstuffs within the digestive system, thus allowing for a greater probability for protein digestion and absorption. Although restrict feeding animals may come at a greater expense due to the additional labor involved, in this study this type of feeding management program proved to be beneficial as a restrict fed feeding program proved to be more efficient from a diet digestibility and utilization perspective.

Murphy, T. A., S. C. Loerch, and F. E. Smith. 1994. Effects of feeding high-concentrate diets at restricted intakes on digestibility and nitrogen metabolism in growing lambs. J. Anim. Sci. 72: 1583-1590.