University of Nevada 2 H E systematic exploration of the application of population T genetics to animal improvement has made available effective and efficient selection techniques and mating systems.
However, suitable selection criteria must be developed before these improved breeding plans can be fully exploited by beef cattle breeders.
Rate and economy of gain and carcass grade and composition are among the important criteria for slaughter animals.
There is considerable evidence indicating that differences in rate and economy of gain may reflect differences in the composition of the increase, which may be determined by differences in mature size.
Guilbert and Gregory (1944) concluded that biased estimates of feed utilization might be obtained when cattle of different mature size were fed on a time constant basis.
Knapp and Baker (1944) suggested correcting to a weight constant basis or feeding to a weight constant basis to obviate errors introduced by time constant feeding.
Kleiber (1936) concluded that total efficiency of energy utilization is independent of body size.
Procter et al. (1934) demonstrated that work efficiency is similar in Shetland Ponies and Percherons.
Brody and Ragsdale (1935) found that dairy goats, Jersey cattle and Holstein cattle convert food energy into milk energy with similar efficiency.
Branaman (1940) found approximately equal T D N requirements per lb.
Of final feedlot weight of lamb produced by Southdowns and Hampshires.
Zeller and Hetzer (1944) noted differences in feed requirements per lb.
Of gain when small, intermediate and large type Poland China barrows were fed to a constant weight (225 lb), but no differences when fed to a constant degree of fatness.
Woodward et al. (1942) found that large type Hereford steers gained faster and used less feed per lb.
Of gain than small type steers when fed for a time constant period.
Washburn et al. (1948) found that conventional type Shorthorn steers gained faster, yet rexThis work is in cooperation with the Animal and Poultry Husbandry Research Branch, A.R.S., U.S.D.A., under Western Regional Project W-1 on beef cattle breeding research.
It was also supported by a grant from the Sears-Roebuck Foundation.
Departments of Animal Husbandry and Newlands Field Station, Reno and Fallon, Nevada, respectively. 109 Downloaded from www.journalofanimalscience.org by guest on May 16, 2013 110 KIDWELL AND iVIcCoR1VLICK quired longer than compact type Shorthorns to reach an equivalent finish.
Feed costs per lb.
Of gain were approximately equal for both types.
Willey et al. (1951) found that when fed for a time constant period regular type Hereford steers gained more rapidly than comprest steers, but except for a greater percentage of shank from the regular steers, there were no significant differences in economy of gain or carcass characteristics.
Stonaker et al. (1952) concluded that, when fed to a constant degree of fatness, there was no significant difference between comprest and conventional type Hereford steers with respect to economy of gain, days on feed, slaughter age, percent of the major carcass cuts, and percent of separable bone, muscle and fat in the 9, 10, ll-rib cut.
The conventional steers gained more rapidly, reached a higher weight, and had a higher dressing percent than the comprest steers.
Knox (1954) reported a decided advantage in lifetime production for large type cows run on semi-arid southwestern range lands.
Since beef cattle are produced under a wide variety of economic and biological conditions, and there is a market requirement for beef produced by many types of cattle, it appears that there may be no single ideal size or type.
It may be necessary to develop several types, each adapted to a particular economic and biological situation.
In order to make intelligent choices of selection criteria it is necessary to know the relations between body size, growth rate, economy of gain, and carcass quality and composition for different types and sizes of cattle.
The purpose of this investigation was to describe the comparative growth, development, feedlot performance and carcass characteristics of Holstein steers, as representing an extreme in size and type, with “regular” or “conventional” Hereford steers.
Materials and M e t h o d s A total of 35 Hereford and 39 Holstein steers were involved in this study.
There were two groups of Herefords, and three of Holsteins.
The first group of 28 Herefords was selected for uniform weight and age as weanling calves.
They were wintered on native mountain meadow hay, ranged during the summer, run on aftermath for 42 days in the fall, wintered on native meadow hay, ranged the following summer, and full fed for 122 days prior to slaughter.
The data included periodic individual weight gains, economy of gain for the group during the feeding period, carcass grade, dressing percent, and percent of five wholesale carcass cuts.
The second group of seven Herefords were selected as typical of conventional long yearling Hereford feeder steers Downloaded from www.journalofanimalscience.org by guest on May 16, 2013 SIZE AND TYPE ON CATTLE GROWTH 111 and individually full fed a fattening ration for 140 days prior to slaughter.
Data include feeder grade, weight gains, feed consumption, slaughter grade, dressing percent, carcass grade, carcass shrink, percent of five wholesale cuts, percent of physically separable muscle, bone and fat in the 9, 10, ll-rib cut and chemical composition of the fat and muscle.
The first group of Holsteins consisted of 19 calves born during a 10-month interval.
They were handled on a standard dairy calf regime, ie, milk and calf starter with access to hay, during the first 23 weeks.
When the youngest of the 12 older calves reached 23 weeks, they were group fed alfalfa hay for 16 weeks.
The 6 younger steers were group fed alfalfa during the last six weeks of this period.
The 19 steers were pastured as a group for 16 weeks, then rotated between feed lot and pasture at 14-day intervals for 16 weeks and fed alfalfa hay for a period of 126 days, and slaughtered.
The data obtained were the same as for the first group of Herefords.
The second Holstein group consisted of 13 steers, handled in a similar manner to the first.
Only growth data were obtained from these animals.
The third group of seven Holstein steers were handled in the same manner as the first two until they were approximately 15 months old.
They were then individually full fed the same grain ration, but slightly different hay than the second group of Herefords, for the same period, and slaughtered.
The same data were obtained.
The data were amenable to analysis of variance and correlation analysis as described by Snedecor (1946).
Results The first group of 28 Herefords and the the first experiment, and the last group of the second experiment.
The second group only to the data used in constructing the first 19 Holsteins constitute 7 Herefords and 7 Holsteins of 13 Holsteins contributed growth curve. Experiment I Figure 1 presents the weight-time growth curves and indicates the differences in mature size.
The more rapid growth of the Herefords up to 35 weeks can probably be attributed to their nursing as compared to the “calf regime” for the Holsteins.
The Hereford curve is subject to fluctuations due to winter feeding and range, while the Holstein Downloaded from www.journalofanimalscience.org by guest on May 16, 2013 112
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