From the February issue: In part 2 of this series (November/December 2014), we discussed using body-condition scoring to monitor energy status in the dairy herd. In this installment, I’ll look at individual feed components and their role in cow fertility and reproductive efficiency.
It was previously mentioned that the late-lactation cow is more efficient at utilizing energy and gaining weight than the dry cow (75 percent versus 60 percent). Therefore, the practice of feeding a low cow ration to a herd of cows that in general is under-conditioned should be discontinued.
This practice is often justified by the assumption that the dairy is saving money on feed costs.
However, the average cow will drop 7.5 pounds of milk when moved to low cow ration that is supposed to meet her requirements. If the low cow ration was $1.00 per cow per day cheaper, the current dry-matter intake for the low cow group is 42 pounds and the milk price is $12.50 per hundredweight, the dairy owner would lose money if the cow dropped more than 2.8 pounds per cow per day when moved to the low group. Not only is this decision to have multiple rations not financially sound, it greatly decreases the chances of late-lactation cows improving their body condition before dry-off.
Another nutritional problem that affects reproduction is the amount of degradable protein fed to the lactating cow. Degradable protein is broken down in the rumen for use by rumen microorganisms. Excessive amounts of degradable protein result in large amounts of ammonia being liberated in the rumen which cannot be utilized by rumen microorganisms and is absorbed into the bloodstream across the rumen wall. To eliminate this excess ammonia from the body, the animal conjugates ammonia into urea in the liver. It is well-known that high levels of blood urea nitrogen and milk urea nitrogen have a direct correlation to the fertility of cows during the breeding period.
Urea is nothing more than two ammonia molecules hooked together. However, this process of conjugating ammonia into urea in the liver requires energy. The more ammonia that is produced in the rumen, the more energy is consumed by the cow to eliminate it from her body. This energy is taken away from the early-lactation cow that already is in a negative energy status. In cases where extremely high levels of degradable protein are being fed, the energy consumed to eliminate the excess ammonia may amount to as much as 7 to 10 percent of the energy required by the early-lactation cow for maintenance and milk production.
Rations that consist of mostly fermented forages will contain higher levels of degradable protein than those with dry hay. All forages should be tested for levels of soluble and degradable protein when formulating the ration so the level of degradable protein can be set at a point where excessive ammonia will not be produced in the rumen. Many molasses products on the market contain urea, and if so, it is important to make appropriate adjustments to the ration. If reproductive efficiency is a problem on the dairy, test for urea levels in the blood (blood urea nitrogen) and milk (milk urea nitrogen). If these levels are above normal, decreasing the amount of degradable protein and adding a bypass protein source such as heat-treated soybean meal, roasted soybeans, blood meal or fish meal should improve conception rates.
It has already been mentioned that energy levels early in lactation are extremely important. If poor-quality forages are fed that are low in energy and digestible fiber, other commodities must be added to compensate for this. Whole cottonseed is often utilized as an important energy source since it contains 17.5 percent fat. Roasted soybeans contain about 18.8 percent fat and are another good source of energy. Animal fats such as tallow can also be added to the ration as an energy source. However, too much vegetable and/or animal fat in a ration may suppress rumen fermentation, so be sure the fat level in your ration is not interfering with rumen fermentation.
Another option is bypass fat. Bypass fat is designed to pass through the rumen without interfering with rumen fermentation and be absorbed in the intestinal tract as an energy source. Most nutritionists agree that the fat level should not exceed 5 to 5.5 percent of the ration if vegetable and animal fat sources are being utilized. If a higher energy level is needed, then bypass fat could be added to fulfill the needed energy requirement.
The importance of a negative dietary cation-anion difference (DCAD) diet has been well documented. Approximately 25 percent of first-calf heifers and more than 50 percent of second-lactation and greater cows will be in a state of subclinical hypocalcemia at the time of calving if they are not being fed a negative DCAD ration. Animals that have subclinical hypocalcemia have blood calcium levels lower than normal but do not show any clinical signs of milk fever. Most dairymen assume that if there is not an issue with milk fever (clinical hypocalcemia) on their farm, then there is no existing problem with calcium metabolism in their cows. This is obviously not true when over 50 percent of the cows may have subclinical hypocalcemia without any clinical signs.
Calcium is necessary for all muscle contraction in the body, including the muscles of the gastrointestinal (GI) tract. If blood calcium levels are lower than normal, contractions of the muscles in the GI tract are less frequent. This slows down the rumen passage rate of feed and results in decreased dry-matter intakes at calving. Decreased dry-matter intake will put the animal in a more-negative energy state causing more weight loss early in lactation. This weight loss will in turn have a negative effect on reproductive efficiency at breeding time.
Calcium is also a very important part of the animal’s immune system. Animals that are suffering from subclinical hypocalcemia will have an increased incidence of infectious disease post-calving, especially with metritis. A recent study showed a 66.6 percent increase in the incidence of metritis in cows with subclinical hypocalcemia when compared to cows that had normal calcium levels in their bloodstream. This will obviously have an adverse effect on reproductive efficiency and delay the time to conception.
In order for the cow to be able to expel the placenta post-calving, she needs to mount an immune response at the site of the connection between the placenta and the maternal tissue of the uterus. White blood cells migrate to this area and basically destroy this connection, thus permitting the placenta to be expelled. All animals with retained placentas, therefore, have a problem with their immune system not functioning properly. Stress and low calcium levels both will have an adverse effect on the animal’s immune system, resulting in an increased incidence of retained placenta. Basically, all animals that have retained placenta will have a uterine infection. Again, this will prolong average days open in these animals and often reduce first-service conception rate. Animals that become sick from uterine infections will also have a decrease in dry-matter intake, resulting in loss of body condition and reproductive efficiency.
In years past, when a dairy experienced a reproductive problem, some type of infectious disease was No. 1 on the suspect list. Progress in the quality of vaccines, vaccination programs and the biosecurity of the dairy herd has greatly decreased the incidence of reproductive diseases in dairy cows. However, these reproductive diseases should always be considered when experiencing a reproductive problem. Nutrition has emerged as the No. 1 reason for reproductive failure in the dairy cow. Evaluating the cow comfort and nutrition of both the dry cows and lactating cows may provide you with the needed information to improve the reproductive efficiency of your dairy herd.
For parts 1 and 2 of this series, refer to the September 2014 and November/December 2014 issues of Bovine Veterinarian, or visit BovineVetOnline.com.