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October 1999
Reproductive Management
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Nutritional Influences On Reproductive Function
by Arun Phatak, D.V.M.
Introduction
As information increases, it is becoming quite apparent that the reproductive function can be influenced by more than simply a deficiency of certain nutrients. Shift in energy status of cows and excessive intake of Crude Protein (CP) or degradable fractions have influenced reproductive performance markedly. In addition, body condition of lactating cows at calving has great leverage over their ability to adjust metabolically to dynamic challenges for increased milk production which, in turn, appears to influence number of days open. Efforts to control these interrelated factors must now be a regular part of nutrition management.

Energy
Energy is the first limiting dietary component for cows in early lactation. Energy demands in the form of milk and body maintenance exceeds energy inputs in the form of digestible feed early post partum. Cows mobilize energy stores from their bodies to make up the difference between energy intake and energy output. This puts cows into a negative energy state. Length of time cows spend on negative energy states vary quite a bit, depending mainly on their ability to increase Dry Matter Intake (DMI) rapidly. Indeed, DMI is much more closely correlated to energy status than milk [Staples et. al. 1990]. Negative energy status of a cow is one of the most important, affecting days to first ovulation. Cows with poor body conditions (negative energy) may not cycle until 60 days post partum, increasing open days.

Lucy et. al. (1991) found that as energy status becomes more positive, early post partum, diameter of the largest follicle on day 10 post partum, increased double ovulation, increase the day of detection of the first Corpus Luteum (CL) was earlier. These changes, thought to be aroused by increases in LH-FSH, insulin, bst, IGF, and other yet to be determined compounds as activated by improving energy status. In order to avoid large negative energy, energy balance, and maximize DMI, well-known conventional management practices are recommended:

  1. Fresh Feed Stuffs
  2. Correct Formulation
  3. Feeding Adlibitum
  4. Higher Feeding Frequency
  5. Adequate Bunk Space
  6. Regular Cleaning of Bunk Space
  7. Shading/Cooling Feeding Area
  8. Monitor Body Condition
  9. Fats 3%-6% of Dry Matter

Supplemental fat may increase energy status thereby improving follicular recruitment and growth. Fat supplement have been shown to increase cholesterol, precurser of progesterone which may increase fertility [Sklan et. al. 1989].


It is becoming quite apparent that the reproductive function can be influenced by more than simply a deficiency of certain nutrients.
Body Condition
Regular body condition score (BCS) will help to improve energy intake if cows are grouped accordingly. Scores are done on a 1-5 scale-1 being thin and 5 being a fat cow. BCS and the loss of BC are important predictors of potential reproductive efficiency. BCS-3 to 3.75 at calving, 2.25 to 2.75 at peak yield, 3 to 3.5 at 150-200 days post partum, and 3.0 to 3.75 at Dry off. Cows which are over conditioned at dry off 7 with a BCS>=4 were 2.5 times more likely to experience reproductive diseases (Dystocia, RFM, Metritis, Abortion) in their next lactation than cows having BCS 3 to 3.5 [Gearhart et. al. 1990]. Cows losing a lot of body condition within a short period of time are candidates for reproductive inefficiencies, rapid body condition loss may result into 10% CR compared to losing BCS slowly [Butler and Smith. 1984]. In general, loss should not exceed 0.5 units in early lactation in order to minimize negative reproductive effects. Cows should gain weight in the late lactation and not during the dry period.

Crude Protein
Protein is required for maintenance, growth, lactation, and reproduction. NRC (1989) recommends dietary concentration of 19% during the first 3 weeks post partum and 16-18% thereafter, depending upon the amount of milk being produced. The reason for higher recommendation (19%) just after calving is low DMI. It is also during this period that cows undergo tremendous metabolic changes, e.g. shifting from a homeostatic to homeorhetic state to prioritize milk production. Demand for glucose is intense and gluconeogenesis is prominent. Protein reserves in the body and tissue are called upon to supply carbon skeletons for glucose synthesis. About 11.4 to 16.0 kg of protein are often mobilized during the first 60 days of lactation [NRC. 1989]. In this conversion of Amiao Acids (AA) to glucose, ammonia is liberated and must be transformed into urea by the liver to prevent ammonia toxicity. Detoxification of ammonia by the liver to urea is an energy consuming process. These processes continue in concert until all protein and energy requirements can be met by diet consumption; this usually does not occur until 6-10 weeks after calving.

 
During these first 10 weeks post partum, cows also undergo tremendous changes as they shift from pregnant to non-pregnant states and prepare to conceive again. The pituitary and hypothalamus undergo changes in control of metabolic and reproductive hormones, uterus undergoes morphological and histological changes, and the ovary undergoes recrudescence, i.e. out-break activity after a period of inactively of follicle recruitment and growth leading to ovulation and formulation of CL. Breeding often id initiated at 8-10 weeks post partum under the influences of this dynamic metabolic scenario. If more protein is consumed than can be effectively utilized, urea (primarily) and ammonia increase in body fluids despite increases in hepatic concentrations or urea cycle enzymes. Urea concentration in blood (BUN) was increased on average 2.54 gm/100 ml for each pound of dietary CP intake (Figure 1). [Canfield et. al. 1990]. These estimations can vary depending upon stage, production, feeding, and percentage of UIP. Urea will also diffuse in body fluids and accumulate in other parts of the body, including the reproductive tract. Increasing CP from 13% to 20% increased urea in vaginal mucus from 7.6 mg to 19.0 mg/ 100 ml. Urea [Holtz et. al. 1986. Caroll et. al. 1988] Table 2 shows that conception rates were higher in cows fed 13-16% protein (64%) than cows fed 19 to 21% CP (52%). Older cows are likely to be affected more than younger cows [Caroll et. al. 1988. Ferguson et. al. 1986 Kaim et. al. 1983].

Mechanisms by which these negative effects occur are not clear. Concentration of ammonia/urea or another unknown nitrogenous compound can be sufficiently high in the body tissue to hamper fertilization, embryo development, and implantation of the conceptus, thereby retarding genesis of a new calf. Some studies show that P4 concentrations in cows fed 15-20% CP were lower than cows fed 13% CP. Feeding high amounts of protein increases concentrations of nitrogenous compounds in blood and vaginal mucus. Urea has proved toxic to ova and sperm (Figure 3). It has also been reported that increases in ammonia concentration can affect the immune system adversely [Targowski. 1983]. Cows fed high protein diets with high DIP have less ability to resist uterine infection [Anderson & Barton. 1988]. Early post partum cows fed 20% CP diets had more reproductive health problems than cows fed 13%. Unhealthy cows fed with high amounts of CP had nearly double the days to first ovulation (37 vs. 16 days) than cows fed low CP (Figure 4). The immune system was affected only mildly at 110 PP by diets differing in DIP. Cows fed 20% CP diets containing 75.5% DIP had a depressed number of platelates and neutrophils but similar numbers of lymphocytes eosinophils and basophils as cows fed 56% DIP diets [Garcia-Bojali et. al. 1992].

 
Progesterone is thought to stimulate production of immune-suppressive uterine proteins [Fisher et. al. 1985] if P4 is depressed by the presence of high amounts of nitrogen compounds, then localized immunosuppressive effects within the uterus may be attenuated leading to rejection of the embryo as a foreign body [Anderson & Barston. 1988].

Stress
Amount of stress may play a key role on whether a high protein diet exerts negative effects. A weakened immune system of older cows compared with young animals may account for their susceptibility to CP toxicity. Cows in negative energy balance may be the most susceptible to reproductive problems from elevated intakes of dietary CP and rumenally degradable protein. If cows are in negative energy status and the liver is expected to detoxify a lot of ammonia which is an energy costly operation.

Vitamins And Minerals
Most of the dietary cow diets are generally provided with adequate vitamins and minerals. Continuous analysis should be done on the feed ingredients to avoid vitamin and mineral marginal deficiencies. Unless sense deficiencies are created, rarely is reproductive efficiency affected. There are several mineral-vitamin supplements available in the market that claim to improve fertility. These should be purchased with thorough investigations. In certain areas of the world, Cu, Co or Se deficiencies are diagnosed. In these instances, extra care must be taken to supplement the diet with required micro-minerals or vitamins. It is also essential to monitor molybdenum contents of the fees which binds available copper.

 
Conventional Management Practices to Avoid Large Negative Energy Balance and Maximize DMI
Fresh Feed Stuffs
Correct Formulation
Feeding Adlibitum
Higher Feeding Frequency
Adequate Bunk Space
Regular Cleaning of Bunk Space
Shading/Cooling Feeding Area
Monitor Body Condition
Fats 3%-6% of Dry Matter
 
 
Conception Rates with Varying Crude Protein Percentages
Reference % Dietary CP
13-16 19-21
Jordan & Swanson 1979a1,2 53 40
Folmantal (1981)  56 44
Kaimetal (1983)2 57 43
Howardetal (1987) 87 85
Carrolletal (1988)3  64 56
Calfledetal (1990)2 48 31
Bruckentaletal (1990)2 65 52
Butler and Etrol (1991)2,3
Average 64 52
Key: 1=of cows conceiving, 2 = P< .05, 3 = 1st service
 
Effect of Dietary C.P. Concentration on Days to 1st Ovulation in Healthy Cows and Those That Have Reproductive Problems
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Potential Inflluences of Energy Status, Dietary Long Chain Fatty Acids, And Exogenous bST on Ovarian Function
 

Relationship Between BUN Concentrations and Intake of Crude Protein
 
References
  1. ANDERSON, G.W. and B.A. BARTON. 1988. Reproductive Efficiency: Potential Nutrition-Management Interactions. Page 107 In Proc. Winter Dairy Management Schools. Cornell University Animal Science. Mimeo. 104.
  2. BUTLER, W.R. and C.C. ELROD. 1991. Nutrition and Reproduction Relationships in Dairy Cattle. Page 73 in Cornell Nutrition Conference. Ithaca, N.Y.
  3. BUTLER, W.R. and R.D. SMITH. 1989. Interrelationships Between Energy Balance and Post Partum Reproductive Function in Dairy Cattle. J. Dairy Science. 72:767.
  4. BUTLER, W.R. and R.W. EVERETT, and C.E. COPPOCK. 1981. The relationship Between Energy, Balance, Milk Production, and Ovulation in Post Partum Dairy Cows. J. Animal Science. 53:742.
  5. CANFIELD, R.W., C.J. SNIFFIN, and W.R. BUTLER. 1990. Effects of Excess Degradable Protein on Post Partum Reproduction and Energy Balance in Dairy Cattle. J. Dairy Science. 73:2342.
  6. CAROLL, D.J, B.A. BARTON, G.W. ANDERSON, and R.D. SMITH. 1988. Influence of Protein Intake and Feeding Strategy on Reproductive Performance of Dairy Cows. J. Dairy Science. 71:3470.
  7. FERGUSON, S.D., T.L. BLANCHARD, S. SHOTZBERGER, and W. CHAPULA. 1986. Effect of Rumen Degradable Protein of Fertility. J. Dairy Science. 69 (Supplement 1):121.
  8. FISHER, C.J., T. GIMENEZ, and D.M HENDRIKS. 1985. Immunosuppressive Activity Associated with Early Pregnancy in Bovines. Biol. Reprod. 34:894.
  9. GARCIA-BOJALIL, C.M., P.J. HANSEN, C.R. STAPLES, W.W. THATCHER, and J.D. SALVO. 1992. Effects of High Protein Degradability and Calcium Salts of Long Chain Fatty Acids in Blood Leucocyte Profiles and Skinfold Responses to Phytohemagglutinin (PHA) in Lactating Dairy Cows. J. dairy Science. 75 (Supplement 1):237.
  10. GEARHART, M.A. C.R. CURTIS, H.N. ERB, R.D. SMITH, C.J. SNIFFEN, LE.E CHASE, and M.D. COOPER. 1990. Relationship of Changes in Condition Scores to Cows Health in Holsteins. J. Dairy Science. 73:3132.
  11. KAIM, M., Y. FOLMAN, H. NEUMARK, and W. KAUFMAN. 1983. The Effect of Protein Intake and Lactating Number on Post Partum Bodyweight Loss and Reproductive Performance of Dairy Cows. Animal Prod. 37:229.
  12. LUCY, M.C., C.R. STAPLES, and W.W. THATCHER. 1991. Energy Balance and Size of and Number of Ovarian Follicles Detected by Ultrasonography in Early Post Partum Dairy Cows. J. Dairy Science. 74:473.
  13. NATIONAL RESEARCH COUNCIL. 1989. Nutrient requirements of Dairy Cattle. 6th Revised Edition. National Academy of Science. Washington, D.C.
  14. SKLAN, D.E. BOGIN, Y. AVIDAR, and S. GURARIE. 1989. feeding calcium Soaps and Fatty Acids to Lactating Dairy Cows: Effect on Production, Body Condition, and Blood Lipids. J. Dairy Res. 56:675
  15. STAPLES, C.R., W.W. THATCHER, and J.H. CLARK. 1990. Relationship Between Ovarian Activity and energy status During the Early Post Partum Period of High Producing Dairy Cows. J. Dairy Science. 73:938.
  16. TAGOWSKI, S.P., W. KLUCINSKI, and D. JAWORCK. 1983-4. Effect of Ammonia on Viability and Balstogenesis of Bovine Lymphocytes. Vet. Immunol. Immunopathol. 5:297.
  17. VILLA-GODOY, A., T.L. HUGES, R.S. EMERY, L.T. CHAPIN, and R.L. FOGWELL. 1988. Association Between Energy Balance and Lukeal Function in Lactating Dairy Cows. J. Dairy Science. 71:1063.
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