Effects of high starch vs. high fiber supplements on carcass characteristics of early-weaned calves

By B.M. Rainey, J.A. Paterson, M.C. King, T.T. Standley, and W.T. Choat, MSU Department of Animal and Range Sciences

Why early wean calves?
Early weaning is commonly practiced during periods of drought when forage availability may be limited and energy requirements of the cow are elevated due to the demands of lactation. Early weaning has been shown to result in a greater percentage of calves that grade Choice or higher and heavier weight calves compared to normal weaning at approximately 210 d of age. Early weaning has lower feed intakes and better feed conversions, resulting in a lower cost of gain, as well as younger calves at slaughter. Likewise, cow performance increased as cow weight and condition score were increased from early weaning progeny.

Does early weaning affect ruminal bacterial populations?
"Normal" weaning occurs at about 7 mo of age, compared to early weaning, which is generally practiced after about 6 wk of age. Calves weaned at less than 6 wk of age have been shown to have a higher concentration of total ruminal volatile fatty acids and a lower ruminal pH when fed a highly palatable pre-starter diet from 3 d of age to weaning. Lengemann and Allen (1959) observed a delay in the onset of typical ruminal microflora and establishment of protozoa (Singh, 1972) from prolonged milk feeding. This suggests that rumen microbes will adapt to the available substrates, making it possible to feed calves much like growing and finishing cattle.

What are the changes in fat deposition for early weaned calves?
Feeding high grain diets, compared to forage- based diets, has been shown to reduce the size of fat cells (adipocytes) but increase the numbers of cells within the longissimus dorsi muscle area. Marbling score correlates more with the number of adipocytes/ gram of tissue rather than the diameter of the adipocytes themselves. Previous work (Cianzio et al., 1982) suggested that a low subcutaneous fat thickness did not necessarily predict reduced marbling, and that intramuscular fat was not a later developing tissue. This research suggested that a simple measurement of backfat thickness at a young age may be used predict the potential of the animal to express in the feedlot phase.

What was the design of the experiment?
Steer calves born between February and March were weaned at approximately 74 days of age. Seventeen steer calves were adapted to a diet containing 60% light barley grain, while 18 steer calves were adapted to a diet containing 60% wheat middlings (Table 1).

Table 1. Ingredient and nutrient composition of diets fed to early-weaned calves

At time of weaning, all calves were weighed and ultrasounded (Classic Scanner 200) to determine subcutaneous and intramuscular fat and longissimus muscle area at the 12th rib. Ultrasound measurements were repeated approximately every 28 days until steers were shipped to a commercial feedlot (90 days after weaning). When steers were harvested, complete carcass data were collected (307 } 7 days after weaning).

What were the results?
There was no sickness or mortality from the time of weaning until the calves were sent to the commercial feedlot. There were no differences in initial body weights, daily gains from birth to weaning, rib eye area or subcutaneous or intramuscular fat at time of weaning. Rate of gain was faster during the first 34 d post- weaning for barley-fed calves compared to wheat midds-fed calves (2.84 lb/d vs. 2.18 lb/d). However, for the entire 90 d growing period gains were similar between treatments (average of 2.87 lb/day). The barley-fed calves did deposit more marbling early and retained this until shipment (4.44 vs. 3.31 % ether extract; Figure). However, by time of harvest, calves fed the wheat middlings during the first 90 days after calving caught up with the barley- fed calves and differences were not significant. These data are inconclusive as to why barley calves initially deposited a greater amount of i.m. fat during the first 34 days after weaning compared with the wheat midds fed calves. By the time of harvest, differences had disappeared. (Figure 1). Wertz et al. (2001), suggested that in order to optimize the advantages of early weaning, calves must be fed increasing amounts of dietary energy in order to maximize performance and attain higher quality grades so that they can be harvested as calf-feds.

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Return to regular view	Text-only	Updated: 08/14/2009