Balancing Ration Needs
Body condition scoring adds another tool to your kit for pinpointing and solving feed management issues.
Scoring the body condition of your cows to evaluate their fatness or thinness according to a five-point scale can be useful to help you make nutrition and health decisions. If you do it regularly, you can pinpoint problems, decrease your feed bill and increase milk production.
Body condition scoring (BCS) generally reflects a dairy cow's energy balance. You generally see negative energy balance at the start of lactation. The cow has a high energy demand and low energy input from feed. She can't eat enough to meet her output requirement, and her body draws on fat reserves to make up the deficiency. The cow then loses weight, becomes susceptible to metabolic disease and doesn't rebreed as fast.
BCS can quickly estimate subcutaneous fat in the dairy cow and has been shown to be as efficient as ultrasound. The Canadian system uses a 1 to 5 system, with 1 meaning thin and 5 meaning fat. The U.S. system is similar, except it's spread over a l-to-9 scale. You can evaluate each cow many times, but the three critical periods are during the dry period, at the beginning of lactation and around the middle of lactation four to five months after calving.
Average scores within your herd can provide information you can use to make management decisions. For example, a group getting too much energy in late lactation results in cows that are too fat during the dry period. Or, perhaps, a group is getting insufficient nutrition going into lactation. You can figure out an overall picture of the herd from averages.
Many studies have looked at the impact of condition on performance. A large body condition loss, for example, can negatively impact rebreeding because of reduced luteal activity. Another study showed cows with a BCS of 3.25 before calving lost less than 0.75 BCS units in the first two months of lactation, and had better metabolic status than cows losing more than 0.75 BCS in the same period. Cows generally should score 3.0 to 3.5 on the l-to-5 scale at the end of the dry period.
A recent Quebec study examined the records of 616,579 Holsteins and 30,519 Ayrshires. Field staff from Valacta, the province's milk recording organization, collected BCSs using the l-to-5 scale in 0.25 increments during the first 150 days of each cow's lactation. A classification model was developed, including the fixed effects of herd, year of calving, month of calving, age at calving and days in milk compared to body condition scoring. This data let researchers develop lactation curves for BCS to help monitor energy balance during lactation.
Ayrshire cows, at an average 3.07, had a slightly higher BCS than Holsteins at 2.93. This difference may be explained by the Holsteins' generally greater milk production. More production theoretically leads to a cow using more of her body reserves. As well, first lactation heifers scored a higher BCS curve than second-lactation cows. This trend reversed for the third and subsequent lactations, as scores increased thereafter.
The study suggests producers raise their heifers in good condition to calving. During the first lactation, however, these animals draw body reserves down too low. They don't have the opportunity to rebuild reserves before second calving as they continue to mature and grow.
In this study, cows lost an average of 0.24 points of BCS for the first 60 days in milk, although BCS started to increase after 50 days in milk. It seems the energy balance becomes positive at six to eight weeks of lactation. BCS generally scores lowest at a negative energy balance of zero. As the energy balance turns positive, cows begin to put back into reserve the fat they have, literally, milked off their backs.
One trend brought out in the Quebec study was cows calving in summer generally had a higher BCS than cows giving birth in winter.
The study showed BCS fluctuated throughout lactation and differed according to age of the animals and their physiological state. This seems to track the negative energy balance modern dairy cows go through during lactation.
To maintain or increase BCS during critical periods, each cow needs enough space at the feed bunk. When feed costs go up, you may be tempted to cheat far-off dry cows by feeding them low-quality forages. However, if their BCS is too low going into lactation, rebreeding, production and health can be affected.
Continually scoring cows for body condition and evaluating your herd for deviations from averages or norms can help you balance your cows' needs with their rations. By developing standard BCS curves, you may be able to detect metabolic disorders, fertility and nutritional deficiencies more easily than by trying to monitor negative energy balance.
Phenotypic Study of body condition scores in Canadian dairy cattle. Moro-Mendez, J., Cue, R.I., and Monardes, H.G. 2008 Can.J. Anim. Sci. 88:213-224 :
This article first appreared in the March 2009 Ruminations column of The Milk Producer magazine.
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