The effects of nutritional treatment, breed and postmortem ageing on growth performance, meat quality and the expression of proteolytic enzymes including the matrix metalloproteinases
Inconsistency in beef quality is a major problem impacting the Ontario beef industry. One of the contributing factors may be age at slaughter due to the diverse nature of management/nutritional programs that are used in the North American beef industry today. Beef cattle for the high quality, grocery and hotel/restaurant trades are marketed for slaughter at a wide range of ages. The specific animal age at slaughter is dependent on the exact nutritional program that each animal is managed under from weaning to slaughter. Age at slaughter is a crucial consideration for past lucrative markets in Japan which insists on beef products from cattle under 21 months of age. Nutritional programs for feedlot cattle may include high grain diets soon after weaning to promote rapid rates of gain and fat deposition and younger ages at slaughter. In contrast, restricted feeding programs incorporating forages may be used for a significant portion of a given animal’s life that results in slower rates of growth and older ages at slaughter. Growth rate may have a significant impact on meat quality due to effects on the quantitative biochemical enzymes and enzyme inhibitors that affect postmortem tenderization. Breed, sire, and dietary factors may influence growth rate and thus, beef tenderness. This project examined nutritional program, breed, and sire effects on growth performance, carcass characteristics, meat quality and biochemical processes that affect postmortem tenderization.
Seventy-two head of cattle (steers) were purchased from Ontario cow-calf producers to provide cattle from 8 sires with 9 half-sibs per sire representing 2 sire breeds, Angus (4 sire groups) and Charolais (4 sire groups). The cattle were allocated to one of 3 nutritional management treatments (regimes) such that each management regime included 3 half-sibs from each of the 8 sires. The 3 management regimes included: 1) a high grain diet (77% high moisture corn) fed ad libitum throughout the trial, 2) limit-feeding of the 77% high moisture corn with intakes restricted to 1.7% of body weight for the first 84 days on feed followed by ad libitum feeding of the diet until slaughter, and 3) limit-feeding of a 93% alfalfa silage diet with intakes restricted to 1.7% of body weight for the first 154 days on feed followed by ad libitum feeding of the 77% high moisture corn diet until slaughter. The 3 management regimes were designed to produce 3 diverse rates of gain for the first 84 days on feed with genetics controlled, followed by expected compensatory growth in cattle that have been initially restricted (limit-fed) and then placed on the high grain diet ad lib. One of the management regimes (93% alfalfa silage diet) was also designed to incorporate an extensive period of backgrounding cattle on a limited plane of nutrition before cattle were finished on a high grain diet. Cattle were fed until they achieved approximately 10 mm backfat as determined by ultrasound.
Cattle backgrounded on the alfalfa silage diet gained less weight than cattle starting the trial on the 77% high moisture corn diet. However there were no differences in average daily gain (ADG) versus cattle fed the high grain diet ad lib versus cattle limit-fed the high grain diet for the first 84 days on feed. These data suggest that feedlot producers could lower feed costs with limit feeding of a high grain diet for a period of time before placing cattle on full feed. There were no breed differences in ADG with gains of approximately 1.8 kg per day across the 3 nutritional management regimes. A diet by breed interaction was present due to similar performance between Angus and Charolais when cattle were started on high grain diets (ad lib or limit-fed), while Charolais gained better over the course of the trial than Angus when started on the alfalfa haylage diet. Carcass traits were similar between cattle fed the high grain diet ad lib versus cattle limit-fed the high grain diet for the first 84 days on feed. Cattle backgrounded on alfalfa haylage had lighter carcasses, less backfat, less marbling, and lower amounts of intramuscular fat than cattle started on the high grain diet. Part of this difference may be attributed to slaughtering some of the cattle backgrounded on alfalfa haylage before they attained the 10 mm backfat endpoint. Grade fats average 9 mm for cattle backgrounded on alfalfa haylage versus 10 mm for cattle that started the trial on the high grain diet. Charolais sired cattle has less grade fat and intramuscular fat content than Angus sired cattle.
Shear force, an instrumental measure of tenderness was affected by diet and breed. Limit feeding of either the high grain or alfalfa haylage diets at the start of the trial decreased beef tenderness versus cattle started on the high grain diet on full feed. Angus-sired cattle produced more tender beef than Charolais-sired cattle. A diet by breed interaction was found with shear force due to relatively similar shear force values for Angus-sired cattle started on limit-fed diets versus Charolais cattle started on limit-fed diets.
Beef was aged for 2, 7, 14, and 21 days to examine effects on tenderness. While beef tenderness increased as beef was further aged, the problems with beef tenderness found in the diet by breed interaction were sustained. The significance of the project’s findings include that limit feeding of high grain diets for 84 days at the start of finishing can result in similar ADG and times on feed as cattle placed on the high grain diets on full feed. This provides the producer with the opportunity to lower feed costs by limit feeding. However beef tenderness problems may be encountered with limit feeding of high grain or alfalfa silage diets at the start of the feedlot phase. The increased toughness with limit feeding can not be corrected by ageing the meat for up to 21 days and is more of a problem with beef from Charolais versus Angus-sired cattle.
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