Recent research suggests genetic selection for milk production in dairy cows has inherited a price – reduced reproductive efficiency.

As the market paradigm changes and the focus sets on total operation efficiency, reproductive performance plays an increasingly important role on the longevity and economic sustainability of the dairy operation.

Inherent reproductive traits, long recognized as low, created the need for technology and management advancements focused on assisted breeding methods to improve reproduction parameters and decrease culling due to fertility problems.

In the last few decades, nutrition interactions have been identified as one of the major role players in physiological and metabolic mechanisms affecting reproductive efficiency.

The role of nutrition
Reproductive efficiency can be altered by intricate physiological mechanisms caused by nutrient imbalances and compensatory intake failure in high-production, early lactation dairy cows.

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Common effects easily recognized in most commercial operations include: heifers provided with low-energy diets perform poorer than their expected reproductive ability; fat dry cows associated with transition metabolic problems; and low conception rates in high-producing cows.

The high nutrient requirements for growth and/or milk production trigger metabolic and endocrine signals that negatively impact reproductive function.

Energy, protein and specific micronutrients, such as vitamins and minerals, are some of the most limiting factors affecting reproductive function.

Energy balance
Several metabolic parameters have been shown to play a role in the relationship between energy balance and postpartum reproductive efficiency.

Maintaining adequate energy balance, particularly postpartum, represents a challenge. This is due to the high metabolic activity characteristic of this stage and is heightened by the slow response to increase compensatory intake in early lactation.

Low energy intake decreases plasma glucose, insulin, progesterone and glucose-dependent follicular growth factors that compromise ovarian activity. Silent estrus and/or anovulation can occur more frequently, reducing heat detection and conception rates conducive to reproductive failure.

Protein utilization
Excessive protein in the diet, particularly in the form of rumen degradable protein (RDP) has been shown to have a negative impact in uterine function and conception rates due to the increase of urea nitrogen (N) in blood or milk.

The detoxification mechanism of ammonia into urea requires energy and the liver’s ability to convert propionic acid into glucose. This may aggravate an existing energy shortage, resulting in reduced ovarian activity.

An adequate energy and protein balance, which maximizes rumen function and efficiency, are key to reduce excess blood nitrogen that impairs reproductive function.

Monitoring excess protein levels and testing cows for milk urea nitrogen (MUN) helps to assure that the protein and carbohydrate fractions are well balanced.

Minerals and vitamins
Mineral and vitamin balance in transition diets have a role in the prevention of problems in the peri-parturient period. Hypocalcaemia, mastitis and lameness have a negative impact on uterine function and fertility.

Proper Ca-to-P ratio influence calcium metabolism and may help to prevent hypocalcaemia. Adequate trace mineral supplementation can prevent early lactation metabolic disorders and signs of deficiency, such as delayed onset of estrus, inactive ovaries and repeat breeding problems.

Supplementation for vitamins E, A and D and selenium deserve special attention due to their role in maintaining antioxidant function, supporting tissue integrity post-partum and promoting immune function.

Management considerations
A sound nutrition program is only one component of a successful reproductive program and cannot correct reproductive inefficiencies caused by poor management.

Hygiene at calving, incidence of metabolic disorders, heat detection accuracy and proper A.I. timing techniques are essential for improving reproductive efficiency.

Proper dry and close-up cow management is the foundation for a successful reproductive program. Meeting the nutrient requirements for late gestation and assuring adequate body condition at calving prevents the incidence of metabolic disorders, dystocia, retained placentas and uterine infections in the transition period.

Sustaining a proper energy balance by encouraging intake, feeding high-quality forages, increasing the concentrate of the forage ratio and adding dietary fat supports a higher metabolic and endocrine status in dairy cows.

Anti-nutrition factors such as mycotoxins (zearalenone, aflatoxin) and gossypol can also play a considerable negative impact on fertility. Feedstuffs should be monitored for contamination.

Overcrowding and negative social interaction should be managed as this has a significant impact on DMI and can reduce signs of estrus.

Conclusion

• There is an important economic advantage to be gained by improving reproductive efficiency in dairy herds.

• Several relationships between nutrition and reproduction have been identified.

• Balancing diets for adequate protein, energy, trace minerals and vitamins are fundamental for improving reproductive performance.

• Attention to management in the dry and transition period, in conjunction to a sound nutrition program, can prevent the occurrence of peri-parturient problems that impair reproductive ability. PD

Pedro Caramona