EQUATION OF REPRODUCTION CHAPTER 1 EQUATION OF REPRODUCTION As we begin this course, I would like to start with an equation of reproduction containing 4 variable and independent factors. Focusing on these and managing them will help assure a successful program!

FOUR FACTORS A = % of Herd Detected in Heat B = Inseminator Efficiency in % C = Herd’s Fertility Level in % D = Semen Fertility Level in % These 4 factors are critical to determining the pregnancy level of a herd.

Total Can NOT be Larger Than the Smallest Percentage % PREGNANCIES Product of Four Factors A x B x C x D = % pregnancy Total Can NOT be Larger Than the Smallest Percentage To determine the percent of pregnancies to be expected from a one cycle breeding, you multiply the factors. In other words: A x B x C x factor D = percent pregnancies. Notice that this is not an average, but a product of multiplication. The total cannot be larger than the smallest percentage in this equation. Now, let’s take a look at the factors. As we do think of the ways we can manage these factors to maximize each of them.

FACTOR A Recovery Interval Since Calving Percent Heat Occurrence Percent Cows in Heat that are Detected Nutritional Adequacy Before and After Calving Factor A is the percentage of cows that are detected in heat. This will be directly affected by the recovery time since calving. Cows return to heat in the order they calve, first calf heifers will require more time. Have we allowed enough time? (45 days minimum for cows.) The percent of cows that show heat or heat occurrence and the nutritional adequacies of the cow herd before and after calving. A cow’s order of life is 1) to get enough feed to survive, 2) to reproduce if number 1 is met, and 3) to produce enough milk to raise her calf. Declining body condition adversely affects estrus and fertility.

FACTOR B Inseminator’s Competency Proper and Hygienic Handling of Semen Placing Semen on Target Factor B relates to the inseminator’s competency. Does he or she handle the semen properly? Do they use good hygiene? Are they placing the semen on target; and, what is their level of experience? Will you be as efficient next week when you go home as you will be a year from now? Remember the inseminator can talk back.

FACTOR C Freedom From Disease Herd Management Efficiency Length of Postpartum Waiting Period Postpartum Metabolic Disease Change in Body Condition Score Factor C relates to the fertility level of the cowherd. Is the herd free from disease? Is the herd on a herd health program of vaccinations and parasite control? What’s the herd management efficiency? What has been the length of postpartum waiting period? Were there any metabolic diseases postpartum? Did the body condition scores change postpartum?

FACTOR D Capability of Bulls to Produce Quality Semen Competency of Laboratory Processing Procedures Frozen Semen Handling Factor D relates to the fertility of semen. Involved in this is the capability of the bull or bulls to produce quality semen. What’s the competency of the laboratory procedures and how was the semen handled as it gets to you and the end user? Is the processor a NAAB member?

Summary 4 Variable & Independent Factors Determine Calving % So, in summary, let’s remember that we are dealing with 4 variable and independent factors. How well we manage each of them will determine the calving percentage of any breeding program

Question 1 A x B x C x D = % Pregnancy What is the equation of reproduction? What factors make up the equation? A x B x C x D = % Pregnancy A = Herd members detected in heat and inseminated (%) B = Inseminator efficiency (%) C = Fertility level of the herd (%) D = Semen fertility level (%)

Question 2 A really poor inseminator with an efficiency of only 60% was working in a herd with very high fertility. In fact the percentages of herd fertility, cows detected in heat and inseminated, and semen fertility were all in the 90’s. Without needing to know the exact figures for these factors you can tell that the percentage of pregnancies resulting from A.I. during this time will not exceed a certain upper limit. What is it? 60%

Question 3 The fertility level in herd X was 90%, but because of poor heat observation techniques, only 65% of the cows were detected in standing heat and inseminated. The bull semen had a fertility rating of 90%. Inseminator efficiency was 90%. What is the percentage of pregnancies resulting from A.I. during this time period? 65% x 90% x 90% x 90% = 47.39%