The agricultural industry and its livestock can be associated with many misconceptions perceived by the public. For example: dairy cows are skinny due to starvation and that beef cows have a high average daily gain because of hormones\steroids.
These agricultural assumptions are not out of the norm. Just like most of society, when I first encountered a dairy "cattle beast" I took note of it's lack of spring of rib, decreased conditioning, and noticeable bone structure, associating this to a malnutrition. However, I was very wrong. Cattle have been a principle building block of human civilization being a source of food and primitive agricultural tool for hundreds of years. Domestication of this beast was estimated to have taken place in the Asian steppes 7000 to 10,000 years ago, and resulted in many changes to the structure of this species. The application of selective breeding lead to the specialization of specific breeds for milk production, meat production, or labor, which yielded stronger more productive animals. To simplify, cows with high milk yield were bred to bulls that had an association with high milking, and cattle with exceptional growth were bred to each other. Eventually, this lead to a differentiation in the structure of beef cattle compared to dairy cattle. Like cattle, dogs also show specialization in particular aspects of structure – you wont see a shih tzu winning any races against a greyhound.
First lets look at the metabolic alterations during the transition from pregnancy to lactation in cows as a species. Entering into the lactation phase, cows undergo physiological changes to ensure provision of adequate nutrients for the calf, and thus nutrient requirements can double overnight. The deficits in requirements are met by the mobilization of body fat and protein, as well as decreasing the use of glucose in non-mammary tissues. These processes are regulated by a pattern of hormonal shifts. For example, somatotropin is increased in early lactation causing increased responsiveness of adipose (body fat) tissue to lipolytic signals such as norepinephrine. The fatty acids are then directly used as fuels by muscle, and/or converted to ketone bodies to be used as an alternative fuel instead of glucose.
Dairy cows have been selected over generations for high milk production, averaging almost 13,500kg of milk per lactation – much more than what a typical calf would require. When milk potential increases, cows have high mammary nutrient needs and eat more feed, however even when fed ad libithum (freely) they cannot consume enough. Consequently, body weight loss increases, debunking the misconception that dairy cows are skinny due to malnutrition.
Beef cattle have been bred to be ‘beefy’ through selective breeding focusing on body condition, weight gain, and reproductive performance. Farmers are paid for the amount of weight yielded by the carcass of a ‘cattle beast’, and thus beef animals cannot have a similar body composition to a dairy animal. Beef cows still use glucose to produce milk, but society has not bred beef cattle for increased milk production, and thus less energy is required for milk during lactation. The extra energy/nutrients are converted into muscle and fat, creating their “beefiness”!
This is not suggesting that producers don’t have too fat or too thin dairy or beef cattle. You can refer to the Body Condition Scoring of Dairy or Beef Cattle for more information on the appropriate condition of these production breeds.
Hope you Enjoyed!