Across Canada, the average conception rate is only 39 percent with pregnancy rate as low as 15 percent. While it is difficult to quantify, estimates of the cost of low conception rates are large.
Increasing 1 percentage point on pregnancy rate will represent around $16.87 per cow per year when pregnancy rate is low. For a 50-cow herd, improved pregnancy rate from 15 percent to 17 percent will represent a savings of $1,600 per year.
What is the relationship between negative energy balance and reproduction?
Researchers have shown that negative energy balance will delay the onset of ovarian cycle after calving, and this will impact pregnancy success during the lactation. Cows that do not ovulate beyond 50 days in milk (DIM) will have increased risk of not getting pregnant by 225 DIM.
Negative energy balance, through its decreased blood glucose, insulin and insulin growth factor (IGF-1), increased blood non-esterified fatty acids (NEFA) and beta-hydroxy butyric acid (BHB) and its liver fat accumulation, will delay the increased secretion of LH and FSH necessary for stimulation of ovulation.
In fact, in a study done with mature cows, ovulatory cows were in a better energy balance status pre-calving and post-calving than non-ovulatory cows. In general, each 0.5 unit (scale one to five) loss of body condition score will show a 10 percent decrease in conception rate.
One of the most important factors to improve energy balance is to maintain higher dry matter intake (DMI) until the day of calving and to rapidly increase intake after calving. Energy intake should be monitored to avoid fat cows during the dry cow period.
A maintained prepartum DMI has been associated with healthier cows when subclinical ketosis (high BHB) and metritis occurrences have been analysed. Increasing the exportation of fat from the liver improves its function, resulting in reduced blood NEFA and BHB levels, and creating a positive impact on reproductive performance.
Liver is also involved in the production of insulin growth factor (IGF-1), an important factor to stimulate the development of ovarian follicles. High blood BHB levels at the first or second week post-calving increased days open from 108 to 124 days.
Some B vitamins are involved in the improvement of energy balance, which benefits reproductive performance. A recent study on commercial dairy herds showed an improvement in energy balance during early lactation, when cows were injected weekly with two B vitamins, folic acid and B12.
For the first 60 DIM, the supplemented cows lost less bodyweight, tended to have a better condition score, and more cows had a milk protein-to-fat ratio more than 0.75, which is an indicator of a reduced negative energy balance. Milk production was unaltered by treatment even if cows apparently mobilized fewer lipid reserves.
This indicated a better energy balance in the B vitamin-supplemented cows. Previous studies by this research group have similarly suggested positive effects of these B vitamins on energetic efficiency.
A research study with 155 dairy cows demonstrated that a blend of protected B vitamins (folic acid, riboflavin and choline) fed during the transition period improved dry matter intake prepartum and reduced blood BHB levels postpartum when compared to a non-supplemented group of dairy cows.
When protected choline alone has been provided, prepartum intakes have been unaffected, suggesting that folic acid or riboflavin may have been involved in this effect.
Minimizing the reduction of prepartum dry matter intake avoids excessive fat tissue mobilization. Both choline and folic acid are methyl donors involved in the exportation of fat from the liver, decreasing blood BHB levels and reducing fatty liver.
The same study demonstrated the benefits to health and reproduction during the transition period. In this research trial, there was a tendency for reduced metritis, a significant decrease in mastitis occurrence and an increased percentage of cows bred at 100 DIM, when cows were supplemented with a protected B vitamins blend (folic acid, riboflavin and choline).
Supplementing B vitamins in early lactation has also been shown to benefit reproductive performance. Researchers in 2012 fed a protected B vitamin blend containing folic acid, pyridoxine, pantothenic acid, biotin and B12, to multiparous Holstein cows from 22 DIM until the cows were confirmed pregnant.
No voluntary waiting period or synchronization program was used in this herd. The supplemented cows had a higher first-service conception rate. Early embryonic losses were similar for both groups.
Moreover, because the cumulative number of cows pregnant at day 200 was not different between treatments, it shows that cows got pregnant earlier with the protected B vitamins. Of economic importance, cows receiving the supplement had their culling rate reduced by 20 percent compared to the control group.
This recent research supports supplementing protected B vitamins to improve reproductive performance. Some of the obtained benefits are indirect effects on metabolism due to improved energy balance, better liver health and immune function.
B vitamins are essential nutrients and their supplementation, protected from rumen degradation, represents a real opportunity in dairy nutrition to optimize reproductive performance. A suggested synergy exists between them and the dietary supplementation of the rumen-protected B vitamin blends is an innovative, proven and practical tool under commercial conditions. PD
References omitted due to space but are available upon request. Click here to email an editor.
- Helene Leclerc
- Technical Support and R&D – Ruminant Nutrition
- Jefo
