By: Dr. Joe C. Paschal, Retired Extension Livestock Specialist & Professor Emeritus
As I related last month, I will discuss the Texas Adapted Genetic Strategies (TAGS) series developed by Dr. Stephen Hammack and others. Last month I discussed the first, this month I want to cover the third in series, Size and Milk. Much of what is in the series will be very useful to Brahman breeders and their commercial and purebred customers.
Body size and milk potential are considered primary genetic traits in beef cattle production, especially in the Brahman breed. Different sizes and levels of milk production a ect other production functions including nutritional requirements, reproduction, and rate and eficiency of gain.
Measures of size can mislead. Weight is the best measure of body size, but weight can vary primarily due to body composition, or fatness. Differences in fatness can be estimated using Body Condition Scores (BCS), with a single change in a BCS representing an 8% change in weight in mature animals. Another measure of size is height, usually measured at the hip and adjusted for age and sex to calculate frame score. Hip height and frame score are measures of the height of an animal – the animals can still differ in length, width, depth, or composition, making it less ideal as a reliable measure of body size. A third measure is the USDA Standards for Feeder Cattle Grading.
There are three classifications (Small, Medium, and Large) to predict the range in slaughter weight at 0.5 inches of fat thickness. For the purposes of this discussion, weight will be used to indicate size in Brahman cattle. In general, cattle that will be genetically larger at a given age will gain weight faster and convert more efficiently if fed for the same length of time or to the same weight. Cattle of different sizes fed to similar degrees of fatness will have reduced differences in gain and feed efficiency.
Differences in genetic size primarily affect weight at the same level of fatness. Genetically smaller cattle should be grown out (grazed as stockers) before finishing while larger cattle can go directly from weaning to the feedyard. Medium sized cattle can go either way depending on the market. Smaller cattle should be harvested at lighter slaughter weights. Additionally, a larger number of smaller cows can be run on a given piece of land than larger cows, reducing cost of production; however, medium to large size cows and their progeny are generally preferred by the industry, and in some breeds, by breeders and their customers.
As long as those factors are understood, efficiency may not be totally compromised. Efficiency varies little in cattle of various body sizes if fed to the same composition (fatness, marbling score), but there are differences in individuals. Some cattle (of all sizes) can gain more weight on less feed (or more on the same amount). Feed conversion (feed:gain) was the most used measure but gain:feed (feed efficiency) is preferred since higher values equal greater efficiency.
Residual Feed Intake (RFI) measures the differences between an animal’s actual feed intake compared to what was predicted at a given rate of gain. A negative RFI (less feed was consumed) is more efficient. The 2024 ABBA Bull Development Program at ST Genetics provided RFI values along with standard growth and carcass data. In comparing the effect of weight on prices, heavier calves of similar type, bring less per pound while fed cattle and their carcasses bring the same amount (within the same grade and weight ranges).
This is because younger cattle are more efficient and faster growing than even cattle slightly older. That should be considered in selection for size, depending on the end production phase. The majority of nutrients required to produce a pound of beef in the cow herd are required mostly for body maintenance. Weight is related at all stages of life, heavier calves as weaners or yearlings tend to be heavier at birth and maturity creating problems with calving diffculty and higher cow maintenance costs. In general, there is little difference in effciency in cow sizes in Brahman or any other breed as long as their nutritional needs are met.
Cow size should be optimized with forage availability in commercial and purebred herds. Higher weaning weights can be managed with larger sires on medium to smaller sized cows, but birth weight and calving difficulty can increase. Also, using females from this breeding as replacements will gradually increase cow size and maintenance costs over time. Milk production in beef cows directly benefits producers through increased calf weaning weight. Although it is not biologically efficient, it is economically beneficial since the cow converts low value feedstuffs into milk. Cows that produce more milk have higher maintenance requirements, even when not milking.
Nutrient requirements, both quality and quantity, increase proportionally as milk production increases. On lower quality feedstuffs, there is no benefit (and often a penalty) in using high milk genetics. However, on a high-quality diet, low milk cows may not fully take advantage of the forage available. The genetic potential for milking ability varies widely and should be evaluated in relation to body size within breed.When nutrient requirements are not met, cows lose body condition and reproduction suffers. Calves with lower genetic potential for growth will be fatter and likely discounted if raised by cows with high milk production.
To capture biological and economic efficiency, when forage quality is low and becomes more variable, small-to-medium size cows are best. Lower forage quality favors smaller sized, lower milking, easier fleshing cows. However, if forage quality and quantity is high, calf weight becomes more valuable and increases in both size and milk should be considered. The balance of body size and milk production can be a ected by nutrient costs in the different production phases. If feed is expensive, higher milking cows are less profitable even though their heavier calves are more desirable for feeding postweaning (due to shorter finishing periods).
Inexpensive feed supports production of heavier calves at weaning but lighter calves are preferred postweaning since they can be fed more efficiently and for longer feeding periods. Optimum levels of size and milk are influenced by the number of production phases in an operation. Net income for cow calf producers is often determined when calves are sold at weaning. For producers with more vertically integrated systems (from breeding through carcass or purebred), the benefits of the total system should be considered, not just the economic benefit in a given phase. Various body sizes and levels of milk production can be eficient, depending on production environments, breeding systems, and desired endpoint.
Cows of different sizes and milk could be run together efficiently with skillful management. Body size and milking ability must be matched to production and marketing conditions; biological compatibility and economic success require these to be in balance. If you are interested in reading the bulletin or would like access to the entire set of TAGS bulletins, email me at joepaschal@yahoo.com.
Next Month’s Article: Breeding Systems
