In my last column (September 2014) we looked at the nutritional requirements of the close-up dry cow and their relationship with reproduction. In this segment, I’ll outline the value of body-condition scoring (BCS) for monitoring the nutritional status of cows at each production stage.
One way of monitoring the energy status of early lactation cows is by BCS. Most researchers have recommended that cows go dry at a BCS of 3.25 to 3.50. The dry cow should not lose any condition during the dry period, so recording a BCS at dry-off and at freshening will let us know if the dry-cow program is working as desired. Cows or heifers that lose body condition during the dry period will almost assuredly have an increase in metabolic disease at freshening and a subsequent decrease in fertility during the breeding period.
A general recommendation is that the early lactation cow should not lose more than 0.5 BCS during the first 60 days of lactation. Therefore, another BCS should be recorded sometime around 60 days post-partum to see how the nutrition program is performing for the fresh cow. If early lactation cows are averaging a BCS loss of more than 0.5, both the dry-cow and fresh-cow nutrition programs should be closely analyzed for weaknesses.
In years past, over-conditioned cows have gained the reputation of crashing shortly after freshening. Consequently, dairy owners have developed a fear of having cows go dry too fat or gain too much condition in the dry pen. This fear is not unjustified, as research has shown that over-conditioned cows with a BCS of greater than 3.75 will show a greater decrease in dry-matter intake as they approach parturition than thinner cows. These over-conditioned cows also do not eat as much or return to a positive energy status as quickly post-calving as do thinner cows. Unfortunately, this concern about cows that are over-conditioned often has gone to the other extreme with a high percentage of today’s cows going dry and subsequently freshening at a lower than desired BCS. Cows are not very efficient at gaining weight during the dry period. Even if dry cows are fed the lactating ration during the entire dry period, they would only be able to increase their BCS by approximately 0.5.
Every year the rolling herd averages of dairies in the United States continue to rise. As a result, the overall average BCS across the country is decreasing. It is not unusual for cows that are being milked three times a day and on BST to average over 90 pounds of milk per day. Nutritional management and cow comfort need to be maximized to maintain the BCS in these herds. Cows that go dry too thin do not have adequate fat stores to compensate for the period of negative energy status after freshening. Ketosis is a common occurrence in these situations, which results in a decrease in dry-matter intake during the first two to three weeks of lactation, even if treated. Far-off dry cows need to be put on a higher-quality ration if they are under-conditioned. The dairy owner needs to allow enough time for the udder to shrink down after drying off the cow, and then place the cow on a more energy- and protein-dense ration in an effort to improve her body condition as much as possible before calving. If there are enough cows to justify two far-off dry pens — one for cows in good condition and one for thin cows — it would be very beneficial. However, it is also important to make sure that the cows in the good condition pen do not lose weight while in that pen.
It is extremely difficult to detect weight loss in the dry cow because the fetus is growing so rapidly at this point in time. Consequently, it often goes unnoticed until shortly after freshening, then it is assumed that the weight loss has all occurred after calving. Special attention needs to be paid to the upper body of the dry cow when assessing the body condition. The degree of the depression between the hook and pin bones, the sharpness of these bones and the length of the shortrib (transverse processes of the lumbar vertebrae) that is visible are the best areas to assess weight loss in the dry period. If a BCS is taken at dry-off and again at freshening, I think many dairy owners would be surprised at how many of their cows are actually losing weight during the dry period. This fact alone can account for a high percentage of the conception problems that occur during the breeding period. It is just as important for the dry cows to be fed a well- balanced ration to fulfill their nutritional requirements as it is the lactating cows.
A recent study published in the Journal of Dairy Science also shows a significant effect of body-condition loss in early lactation on first-service conception rates. At 70-day pregnancy diagnosis, the first-service conception rate was 22.8 percent for cows that lost BCS during the first two weeks post-calving, 36 percent for those that maintained their BCS and 78.3 percent for those that gained BCS. Surprisingly, there was no statistical difference in the milk production between these groups. These results also emphasize the importance of good management and nutrition of the pre-partum and early fresh cow and its effect on reproductive efficiency.
In Part 3 of this series, we’ll look at the roles of specific dietary components, including degradable protein, urea, fat and calcium in dairy reproduction.
See more articles about reproductive services, BVD, salmonella and more in the November-December digital edition of Bovine Veterinarian.