Reproduction in Dairy Cattle

INTRODUCTION

A healthy dairy cow delivering a healthy calf these days is the result of top management on a dairy farm. Very few people understand the huge challenge and complexity of achieving optimum reproduction efficiency in a high producing dairy herd.

Firstly, the dairy cows of 2002 are genetically geared for high levels of milk production. Secondly, the heritability of reproduction efficiency (conception rate; calving percentage; intercalving period) is very low ( < 5.0% ). Some modern day geneticists estimate this value to be even less than 2%. In practical terms this means that reproduction efficiency is just about not hereditary at all and that the success of reproduction efficiency is 95 % + dependant on the environment, which in practical terms means that the feeding and management program of a specific dairy herd. It should be clear that the reproduction achievement of any dairy herd is therefore just about totally dependant on management with very little or no help from genetics. This is a huge and complex challenge, especially as cows with 2002 genetics have been bred over many decades to channel all absorbed nutrients and body reserves towards milk production.

THE ON FARM REPRODUCTION EFFICIENCY PROGRAM MUST BE EXCELLENT..

Dairy farmers must understand that for an absolute vital aspect like reproduction efficiency,which is 95 % + management dependent, an excellent and foolproof as possible, practical on farm program must be in place. The goal of this paper is to focus on the nutrition aspects of the program, and especially the trace element supplementation program which is absolutely vital for reproduction success in a dairy herd.

The most important nutrition dependant aspect for reproduction efficiency that must be in place is to ensure that cows will not lose more than one condition score from calving till A.I. (Grummer, 1998). This means cows should calve at a 3.5 condition score and by maximising dry matter intake during the transition period, the dairyman should ensure a condition score of 2.5 or higher at insemination.

• The second most important nutrition aspect for reproduction success in the dairy herd is to have an efficient practical trace element supplementation program in place to ensure optimal trace element functions especially at critical times like mating.

IMPORTANT TRACE ELEMENTS FOR REPRODUCTION EFFICIENCY

The four most important trace elements involved in functions that are essential for optimum reproduction efficiency are:

Zinc

• essential for the onset of estrus
• essential to prevent abortions
• increases plasma beta-carotene levels which is correlated to improved conception rate and embryonic development
• essential for sperm count and quality in bulls

Copper

• essential for conception
• essential to prevent abortions

Manganese

• essential for estrus and normal heat
• essential for normal ovulation
• essential for conception
• essential to prevent abortions
• essential for normal male libido and sperm quality

Selenium

• essential to prevent abortions
• essential for sperm quality in bulls.

FOCUS TRACE ELEMENT SUPPLEMENTATION CORRECTLY

The focus of practical supplementation of trace elements to dairy cows has changed totally from a decade ago. The focus now is on the development of a supplementation strategy which will "optimize" (a very difficult goal to attain) trace element dependant functions that are necessary for optimal health. These include normal ovulation, heat, conception, successful implantation, development of the fetus and ultimately the birth of a strong and healthy calf. This strong production orientated focus attempts to optimize the full range of trace elements rather than the outdated goal of preventing deficiency symptoms of specific trace elements. Hutjens & Tomlinson (2001) demonstrated clearly that a slight decrease in the trace element status of dairy cows from optimal (adequate), results in decreased enzyme functions, immunity, performance and fertility.

• Dairy cows and heifers must be supplemented at all times with at least 150 % of NRC (2001) requirements for all trace elements. A portion (10 to 25 %) of these supplements should be in the form of effective "organic" sources.

• Secondly all cows and heifers should be supplemented with injectable zinc, copper, manganese and selenium (100mg Zn, 100mg Mn, 50mg Cu and 25mg Se) subcutaneously with vitamin A + E intramuscularly, 3 to 4 weeks before calving and 3 to 4 weeks before mating.

The importance of the two injection-supplementation program cannot be overemphasized as they correct for possible ineffective absorption and low or variable intakes. These injections will cause a significantly higher than normal trace element status in the post absorption state of the dairy cow which should result in optimum trace element functions 20 to 30 days after the injection. The simultaneous supplementation of vitamin A + E will also enhance the synergy between vitamin A & Zinc and vitamin E & Selenium to further optimize trace element / vitamin functions.

CONCLUSION

It is recommended that dairy farmers pay serious attention to their trace element supplementation program. They must ensure that dairy meals / complete feeds contain adequate trace element levels which are properly balanced. It is also of utmost importance to "TOP UP" the per os supplementation with two or three vital injections at critical times (three weeks before calving and mating and also possibly drying off).

REFERENCES

Chew, B.P., 2000. Micronutrients play role in stress, production in dairy cattle.Feedstuffs, June 12, 11.
Grummer, R.R. 1995. Impact of changes in organic nutrient metabolism on feeding the transition dairy cow. J. Anim.Sci. 73. 2820.
Hutjens, F.H. & Tomlinson, D. J., 2001. Nutrition important in transtion feeding programs. Feedstuffs, 31 December 2001, page 9.