Research and Reviews: Beef and Sheep

Special Circular 170-99

Effects of Feeding Pelleted, Ensiled, or a Combination of Pelleted and Ensiled Alfalfa on Lamb Growth and Carcass Characteristics

F. L. Fluharty¹, G. D. Lowe, and D. D. Clevenger
The Ohio State University Department of Animal Sciences

Abstract

Seventy-two Rambouillet x Hampshire lambs (initial weight 115.6 ± 0.5 lb) were used in a randomized complete block experiment to determine the effects of alfalfa form and combinations on animal performance and carcass characteristics. Lambs consuming pelleted alfalfa had a 48.8% greater (P < 0.01) average daily gain (ADG) compared with lambs consuming alfalfa haylage (0.61 vs. 0.41 lb/day, respectively). There were no differences (P > 0.10) in feed efficiency or total dry-matter intake (DMI) due to alfalfa form. Lambs fed pelleted alfalfa had a greater (P < 0.05) dressing percentage compared to lambs fed alfalfa haylage. In feedlot situations, processed forages can be used to effectively produce large, lean lamb carcasses. Forage particle size and forage moisture content greatly affect dry-matter intake and animal performance, even when the forage is one species of similar maturity. Days on feed and dressing percentage are both economically important criteria that differ due to form of forage even when feed efficiencies are similar. However, lamb marketings could be spread out over a longer period of time by altering the form of forage fed in forage-based feedlot situations.

Introduction

Lambs that graze alfalfa accumulate less fat on a daily basis than lambs that are fed corn-based diets, but visceral organ weight increases due to the amount of forage consumed and the particle size of the forage. This increase in visceral organ size results in greater maintenance energy requirements of lambs grazing alfalfa, making the conversion of feed energy to protein gain less efficient (Fluharty and McClure, 1997). In feedlot diets, long-stem alfalfa does not mix well with the concentrate portion of the diet and results in sorting in the feed bunk. However, feeding ensiled or pelleted alfalfa should minimize digestive disorders, reduce the need for supplemental protein, and blend well with the concentrate portion of a feedlot diet. Nevertheless, ensiled alfalfa is relatively close to grazed alfalfa in terms of particle size, whereas ground pelleted alfalfa more closely resembles a concentrate feed in terms of particle size. Therefore, differences in performance may exist. The objectives of this experiment were to determine the effects of alfalfa pellets vs. ensiled alfalfa in lamb feedlot diets on animal growth and carcass composition.

Experimental Procedures

Seventy-two Rambouillet x Hampshire lambs (initial weight 115.6 ± 0.5 lb) were used in a randomized complete block experiment to determine the effects of alfalfa form and combinations on animal performance and carcass characteristics. There were 24 wethers and 48 ewes used in the experiment. The experiment began in January of 1999 and ended in April of 1999. The lambs originated from a ranch in Savery, Wyoming, and were transported by truck approximately 1,581 miles to the Ohio Agricultural Research and Development Center (OARDC) sheep feedlot in Wooster, Ohio. Three diets were fed (Table 1). Diets were formulated to meet the dietary nutrient requirements of lambs (NRC, 1985) and to provide equal concentrations of vitamins, ammonium chloride, and lasalocid across treatments. Feed samples (100 g) were collected every 14 days throughout the experiment and composited for analysis. Feed samples were dried in a forced-air oven at 551°C, ground to pass a 2-mm screen, and analyzed for DM (AOAC, 1984).

Lambs were individually weighed, ear tagged, and vaccinated against internal and external parasites with injectable Ivermectin. Initial and final weights of the lambs were determined using the average of weights taken on two consecutive days, and 14-day intermediate weights were taken prior to feeding at 0800 hours. The ADG, DMI, feed efficiency (lb gain/lb feed), and days required to reach slaughter weight were determined for all lambs. Lambs were removed from the trial, on a pen basis, as each pen reached the predetermined terminal weight range of 140 to 150 lb.

There were two blocks of lambs, based on lamb sex and weight. All blocks had four lambs per replicate pen, and there were six replicate pens per each of the three treatments. The pens were 4.9 x 16.0 ft with 4.9 ft of bunk space. All pens were constructed using expanded metal floors, with metal gates on three sides and a wooden fence-line feed bunk on the fourth side. Each pen had an automatic water cup so that water was available at all times.

Feed offered and feed refused were weighed daily in each pen prior to refeeding at 0830 hours. Because sorting was predicted, feed was not allowed to remain in the feed bunk for more than one day before it was discarded. This was done because nutrient content of the diet available to the lambs could differ substantially among the diet groups if sorting occurred. Pens of lambs never had their intake increased or decreased by more than 10% of the previous day’s intake.

All lambs were slaughtered when their pen reached the predetermined terminal weight range to determine final carcass measurements. Lambs were slaughtered at a commercial abattoir. Chilled carcass weights were determined 48 hours after slaughter, and backfat and loin-eye area were measured, and internal fat was estimated.

Statistical analysis was performed using the GLM procedure of SAS (1988) for a randomized complete block experiment that was blocked by pen size. Performance data for the total trial were analyzed using a model that included effects due to diet, block, and the diet x block interaction. Pen was used as the experimental unit for lamb performance data. Individual lambs served as the experimental unit for carcass data. Carcass data were analyzed using a model that included effects due to diet, block, and the diet x block interaction. Treatment means were compared with Fisher’s protected LSD using the PDIFF statement of SAS (1988) when protected by a significant (P < 0.05) F-value. The residual mean square was used as the error term.

Results and Discussion

The effects of form of alfalfa on lamb performance are shown in Table 2. Pelleted alfalfa resulted in a greater (P < 0.01) DMI compared with pellets+haylage, or haylage alone. The combination of pellets+haylage also resulted in a greater (P < 0.01) DMI compared to haylage alone. Therefore, there was an inverse relationship between both forage particle size and diet moisture content with dry-matter intake. Smaller forage particles spend less time in the rumen and reticulum compared with larger particles that may need to be regurgitated and remasticated before they can pass out of the reticulum. The smaller particles with the ground, pelleted alfalfa compared with alfalfa haylage allow for more surface area for ruminal bacteria to attach and digest the feed particles. A faster rate of digestion allows an animal to consume more feed, as there is less undigested feed taking up space in the rumen. Furthermore, the drier feed particles with the pelleted alfalfa compared to alfalfa haylage would mean that the pelleted alfalfa was more energy dense (less space taken up with water). These two factors resulted in lambs consuming pelleted alfalfa having a 48.8% greater (P < 0.01) ADG compared with lambs consuming alfalfa haylage (0.61 vs. 0.41 lb/day, respectively). Lambs consuming the pelleted alfalfa+haylage diet had a 34.1% increase (P < 0.01) in ADG compared with the haylage-fed lambs (0.55 vs. 0.41 lb/day, respectively). Because the lambs were taken to similar terminal weights, the increase in ADG with alfalfa pellets vs. alfalfa haylage resulted in lambs fed the pelleted alfalfa requiring 53.8 days to reach their slaughter weight compared with 60.8 days for lambs fed the alfalfa pellet+haylage diet, and 81.8 days for lambs fed the alfalfa haylage diet alone. There were no differences (P > 0.10) in feed efficiency or total DMI due to form of alfalfa.

The effects of form of alfalfa on lamb carcass characteristics are shown in Table 3. There were no differences in hot carcass weight (HCW), loin-eye area (LEA), or backfat depth due to form of alfalfa. However, lambs fed pelleted alfalfa had a greater (P < 0.05) dressing percentage compared to lambs fed alfalfa haylage, with the lambs fed the combination diet being intermediate, and not different from either of the other two diets. Numerically, dressing percentage decreased as the proportion of alfalfa haylage in the diet increased. The most likely reason for this would be increased undigested feed particles and associated increases in ruminal water with diets containing longer particles of forage. Normally, when high concentrate diets are fed (Fluharty and McClure, 1997), or when high-concentrate diets are compared with alfalfa (Fluharty et al., 1999), increases in DMI result in increases in visceral organ mass and gut contents with resulting decreases in dressing percentage. However, when forages are compared, reductions in particle size, with resulting reductions in ruminal retention time, may override increased DMI when compared with diets containing long forage particles, or relatively indigestible forage particles.

Implications

In feedlot situations, processed forages can be used to effectively produce large, lean lamb carcasses. Forage particle size and forage moisture content greatly affect dry-matter intake and animal performance, even when the forage is one species of similar maturity. Days on feed and dressing percentage are both economically important criteria that differ due to form of forage even when feed efficiencies are similar. However, lamb marketings could be spread out over a longer period of time by altering the form of forage fed in forage-based feedlot situations.

References

AOAC. 1984. Official Methods of Analysis. 14th Ed. Association of Official Analytical Chemists, Washington, D.C.

Fluharty, F. L. and McClure, K. E. 1997. Effects of dietary energy intake and protein concentration on performance and visceral organ mass in lambs. J. Anim. Sci. 75:604—610.

Fluharty, F. L., McClure, K. E., Solomon, M. B., Clevenger, D. D., and Lowe, G. D. 1999. Energy source and ionophore supplementation effects on lamb growth, carcass characteristics, visceral organ mass, diet digestibility, and nitrogen metabolism. J. Anim. Sci. 77:816—823.

SAS/STAT.1988. SAS/STAT User’s Guide: Statistics. SAS Institute, Inc., Cary, N.C.