Research and Reviews: Beef and Sheep

Special Circular 170-99

Effects of Pelleted Alfalfa and Whole-Shelled Corn Combinations on Lamb Growth and Carcass Characteristics¹

F. L. Fluharty²
The Ohio State University Department of Animal Sciences
Ohio Agricultural Research and Development Center

Abstract

Two hundred thirty-four Columbia x Suffolk lambs (initial body weight [BW] 105 ± 0.7 lb) were used in a randomized complete block experiment to determine the effects of alfalfa pellet and whole-shelled corn combinations on animal performance and carcass characteristics. When hay is not fed, receiving diets for lambs should contain no less than 40% ground pelleted forage in order to prevent acidosis and depressed animal performance. There were linear (P < 0.001) increases in daily dry-matter intake (DMI) from day 20 to the end of the experiment and in overall daily DMI (from day one until the end of the experiment) with increasing alfalfa concentration. However, there were linear (P < 0.001) decreases in feed efficiency (gain/feed; G/F) from day 20 to the end of the experiment and in overall G/F (from day one until the end of the experiment) with increasing alfalfa concentration. There was also a quadratic (P < 0.01) ADG response to alfalfa concentration, with the 60% alfalfa diet resulting in the greatest ADG. Optimal average daily gain, days on feed, loin eye area, and carcass fat percentage occurred with diets containing whole-shelled corn and pelleted alfalfa combinations. Optimal feed efficiency occurred with the 0% alfalfa diet; however, the 0% alfalfa diet resulted in lamb carcasses with the most fat. Pelleted alfalfa and whole-shelled corn are more acceptable when fed in combination than when either feed source is fed alone.

Introduction

Lamb feedlot diets are usually offered ad libitum. In the Midwest, corn is the least expensive energy source, and animals offered a high-concentrate diet ad libitum generally have a greater ADG than animals grazed on legumes (Bidner et al., 1981; Tatum et al., 1988; McClure et al., 1994; Murphy et al., 1994). However, lambs that graze alfalfa accumulate less fat on a daily basis than lambs that are fed corn-based diets (Murphy et al., 1994; McClure et al., 1995; Fluharty et al., 1999), but visceral organ weight increases due to the greater amount of forage dry matter consumed compared with corn-based diets (Fluharty et al., 1999). This increase in visceral organ size results in greater maintenance energy requirements, making the conversion of feed energy to protein gain less efficient (Fluharty and McClure, 1997). In feedlot situations, grazing is not practical, and long-stem hay does not mix well with the concentrate portion of the diet. This results in sorting in the feed bunk and inefficient lamb growth. Feeding ground pelleted alfalfa should minimize digestive disorders, reduce the need for supplemental protein, and blend well with the concentrate portion of a feedlot diet. However, there is very little information concerning the effects of pelleted alfalfa in combination with whole-shelled corn where the dietary crude protein concentration was similar across diets and where lambs were taken to equal end weights. The objective of this experiment was to determine the effects of varying levels of alfalfa pellets and whole-shelled corn in lamb feedlot diets on animal growth and carcass composition.

Experimental Procedures

Two hundred thirty-four Columbia x Suffolk lambs (initial BW 105 ± 0.7 lb) were used in a randomized complete block experiment to determine the effects of alfalfa pellet and whole-shelled corn combinations on animal performance and carcass characteristics. The experiment began in September of 1998 and ended in January of 1999. The lambs originated from a ranch in Montrose, Colorado, and were transported by truck approximately 1,582 miles to the Ohio Agricultural Research Development Center sheep feedlot in Wooster, Ohio. Six ratios of alfalfa:corn were fed (Table 1). Diets were formulated to meet the dietary nutrient requirements of lambs (NRC, 1985) and to provide equal concentrations of crude protein (CP), vitamins, ammonium chloride, and lasalocid across treatments. The concentration of phosphorus (P) was held constant at 0.4% across diets. However, because of the high concentration of calcium (Ca) in alfalfa (1.52% on a DM basis) and the potential negative impact on diet palatability of increasing the level of supplemental Ca in diets containing low concentrations of alfalfa, the concentration of Ca decreased as the concentration of alfalfa in a diet decreased. 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 551C, ground to pass a 1-mm screen, and analyzed for dry matter (DM), organic matter (OM), nitrogen (N) (AOAC, 1984), and neutral detergent fiber (NDF) according to Procedure A (Van Soest et al., 1991). On a dry-matter basis, the alfalfa pellets contained 17.82% CP and 47.07% NDF, and the whole-shelled corn contained 8.81% CP and 9.97% NDF.

Upon arrival at the feedlot, the lambs were provided long-stem alfalfa hay and had access to water troughs containing an electrolyte solution. Following an 18-hour rest period, the lambs were individually weighed, ear tagged, and vaccinated against Clostridium perfringens Types C and D and Tetanus, with a second vaccine against Clostridium perfringens Types C and D and Tetanus given 14 days later. 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. Average daily gain, DMI, feed efficiency (gain/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 pen size and the number of lambs in a pen. Block 1 had five lambs per replicate pen and three replicate pens per each of the six treatments. The pens in Block 1 were 4.9 x 16.0 ft with 4.9 ft of bunk space, or 11.7 inches per lamb. Block 2 had 12 lambs per replicate pen and two replicate pens per each of the six treatments. The pens in Block 2 were 9.8 x 16.0 ft with 9.8 ft of bunk space, or 9.8 inches per lamb. 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 was weighed daily in each pen prior to feeding at 0830 hours. Because sorting was predicted, feed refusals were not allowed to remain in the feed bunk for more than one day before they were 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. Lambs were slaughtered at a commercial abattoir. Chilled carcass weights were determined 48 hours after slaughter, backfat and loineye 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. Pen was used as the experimental unit for lamb performance data. Individual lambs served as the experimental unit for carcass data. Data were analyzed using a model that included effects due to diet, block, and the diet x block interaction. Treatment means were compared with orthogonal contrasts when protected by a significant (P < 0.05) F-value (SAS, 1988). The residual mean square was used as the error term.

Results and Discussion

The effects of dietary alfalfa concentration on lamb performance during the receiving phase are shown in Table 2. The DMI increased linearly (P < 0.001) as alfalfa concentration of the diet increased, going from approximately 1.5 % of body weight for lambs fed the all-concentrate diet to 3.5 % of body weight for those fed the 100% alfalfa diet. There was a quadratic ADG response (P < 0.001) to alfalfa with lambs fed the 0 and 20% alfalfa diets losing weight, and lambs fed the 80% alfalfa diet having the greatest ADG. Likewise, there was a quadratic response (P < 0.001) for feed efficiency; lambs fed the 0 and 20% alfalfa diets had a negative feed efficiency as a result of weight loss, and those fed the 60% alfalfa diet had the greatest feed efficiency. Lambs needed at least 40% alfalfa in their diet to have a positive weight gain during the receiving period, and the efficiency and gain responses were optimized with the 60% and 80% alfalfa diets, respectively. Because of the large differences in DMI during this relatively short receiving period, however, part of the differences in ADG were probably due to differences in gut fill.

The effects of dietary alfalfa concentration on lamb performance post-receiving are presented in Table 3. There were linear (P < 0.001) increases in daily DMI from day 20 to the end of the experiment and in overall daily DMI (from day one until the end of the experiment) with increasing alfalfa concentration. However, there were linear (P < 0.001) decreases in feed efficiency (G/F) from day 20 to the end of the experiment and in overall G/F (from day one until the end of the experiment) with increasing alfalfa concentration. There was also a quadratic (P < 0.01) ADG response to alfalfa concentration, with the 60% alfalfa diet resulting in the greatest ADG.

There was a quadratic (P < 0.05) response to alfalfa concentration for days on feed, with the 60% and 80% alfalfa diets resulting in the shortest number of days required to reach the terminal weight (68.8 and 64.6, respectively), and the 0% alfalfa diet requiring the most days (87). Under most feeding situations, the high-concentrate diet would be expected to result in a greater ADG and fewer days on feed compared with alfalfa-based diets (McClure et al., 1995; Murphy et al., 1994). However, in the present experiment, the negative ADG in the receiving period that occurred in the lambs fed the 0 and 20% alfalfa diets resulted in the longer time required to reach their terminal weight even though there were no differences (P > 0.10) in ADG from day 20 until the end of the experiment. There was a linear (P < 0.001) increase in total DMI with increasing alfalfa concentration. However, there were no differences (P > 0.10) in total metabolizable energy (ME) required to reach the terminal weight. The 0% alfalfa diet had NE_m and NE_g concentrations of 2.079 and 1.427 Mcal/kg compared with 1.305 and 0.746 Mcal/kg, respectively, for the 100% alfalfa diet (Calculated energy concentrations based on NRC [1985] values) (Table 1). Therefore, the diets resulting in the greatest intake were the lowest in energy concentration. Growth rate is proportional to energy intake above maintenance, with an increase in energy intake resulting in increased carcass gain as well as fat percentage (Rohr and Daenicke, 1984). A large proportion of an animal’s maintenance energy requirements can be attributed to the visceral organs, especially the liver and gastrointestinal tract (Ferrell and Jenkins, 1985). Visceral organ size has been shown to be affected by the level of feed intake (Burrin et al., 1990; Fluharty and McClure, 1997), and even with highly digestible diets, increases in DMI result in increased visceral organ mass and resulting increases in maintenance energy requirements (Fluharty and McClure, 1997). Therefore, the diets containing higher proportions of alfalfa which resulted in greater DMI than diets containing lower proportions of alfalfa would be expected to result in a greater visceral organ mass and increased maintenance energy requirements. Decreased visceral organ size could partially explain why the 0% alfalfa diet, which had the lowest DMI and greatest feed efficiency, could result in lambs requiring between nine and 23 days more on feed to reach the terminal weight compared with the diets that contained alfalfa, but did not result in more total Mcal of ME being needed.

The effects of alfalfa concentration on lamb carcass characteristics are shown in Table 4. As desired, there were no differences (P > 0.10) in final weight. However, there was a linear decrease (P < 0.001) in hot carcass weight and dressing percentage with increasing alfalfa concentration. Although not measured, one reason for this would be increased visceral organ weight and associated gut fill with increasing alfalfa percentage as a result of increased DMI. Carcass fat percentage is directly related to carcass weight (Berg and Butterfield, 1968; Waldman et al., 1971; Old and Garrett, 1987). Therefore, the linear increase in backfat depth (P < 0.01); percentage kidney, pelvic, and heart (KPH) fat (P < 0.05); and yield grade (P < 0.01) with decreasing alfalfa concentration (increasing whole corn concentration) may be expected based on the differences in hot carcass weight. The increase in fat content in the present study with increasing dietary energy concentration agrees with the findings of Solomon et al. (1986).

However, differences in rumen microbial end-product production due to the large differences in dietary forage to concentrate ratio in the present study probably also played a role in the differences in carcass fat measurements. Rumsey et al. (1970) reported that both changing from an all-hay diet to an all-concentrate diet and increasing the dry matter intake of the concentrate diet from 0.5, 1.0, 1.5, or 2.0% of body weight caused changes in volatile fatty acid (VFA) production in steers. The rumen pH, molar percent of acetate, and acetate to propionate ratio decreased as concentrate intake increased. Conversely, the concentration of total VFA, and the molar percent of propionate increased as concentrate intake increased. Propionate, the only glucogenic VFA (Hungate, 1966, Leng, 1970) is quantitatively the most important single precursor of glucose in the ruminant (Annison and Armstrong, 1970). The production of propionate leads to glucose production, which increases insulin secretion (Bines and Hart, 1984). Insulin, secreted in the pancreas, stimulates the uptake and incorporation of amino acids into protein, inhibits proteolysis, stimulates lipogenesis, and inhibits lipolysis (Bassett, 1975; Bines and Hart, 1992; Weeks, 1986). Therefore, a shift in VFA production toward a higher molar percent of propionate through increasing the proportion of corn in the diet could lead to more fat production (lipogenesis) and be one of the primary reasons for lambs fed the 100% concentrate diet having greater backfat, and greater KPH fat compared with the diets containing a higher proportion of alfalfa.

There were no differences (P > 0.10) in leg conformation score due to diet. However, there was a quadratic response (P < 0.01) to loin-eye area (LEA) with the 40 and 60% alfalfa diets having the largest LEA. In contrast, Crouse et al. (1978) reported no differences in loin-eye area due to energy density in lambs taken to approximately the same end weight. Rohr and Daenicke (1984) stated that live weight gain at a given body weight essentially depends on energy intake; however, when an animal is fed a forage-based diet, the variations in gut fill may be so large as to render live weight gain almost meaningless as a standard measure of growth rate. Based upon the results of this experiment, the ability to predict actual body (carcass) weight of animals offered various concentrations of a ground pelleted forage ad libitum is compromised due to differences in DMI and associated differences in gut fill and visceral organ size.

Implications

When hay is not fed, receiving diets for lambs should contain no less than 40% ground pelleted forage in order to prevent acidosis and depressed animal performance. Optimal average daily gain, days on feed, loin-eye area, and carcass fat percentage occurred with diets containing whole-shelled corn and pelleted alfalfa combinations. Optimal feed efficiency occurred with the 0% alfalfa diet; however, the 0% alfalfa diet resulted in lamb carcasses with the most fat. Pelleted alfalfa and whole-shelled corn are more acceptable when fed in combination than are either feed source alone.

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