What should be the goal for reproductive performance of dairy herds in Virginia?

Dairy Pipeline: October 2002

Ray L. Nebel
Extension Dairy Scientist,
Reproductive Management
(540) 231-4432
email: rnebel@vt.edu

Table 1 was constructed using DairyMetrics reports from DRMS (Raleigh, NC). In Table 1, herds were stratified by Calving Interval (CI) with daily milk yield, Projected 305 day ME milk, days in milk, and various reproductive performance variables listed. Using daily milk yield as an indicative variable a CI of less than 14 months should be the goal. Using Projected 305 day ME milk yield as the controlling variable the ideal CI could be narrowed to 13 to 13.9 months. With each monthly increase in CI above a 13.9 month CI daily milk yield dropped 3 to 4 lbs and projected ME milk dropped almost linearly from 23,652 lbs for a 13 to 13.9 month CI to 20,791 lbs for herds having a CI greater than 16.9 months. Approximately one-third of the Holstein herds (n=1545) had a CI less than 14 months, therefore a CI less than 14 months is an achievable goal that will produce higher daily milk yield and higher milk yield over the length of the lactation. Calving interval is determined by days to first service, heat detection efficiency and conception rate. Herds that obtained a CI less than 14 months averaged less than 83 days to first service and approximately 50% heat detection efficiency (as measured by percent of heats observed) and conception rates above 40% for first service. It is interesting that conception rates at first service ranged from 40 to 47% with herds with either the shortest or longest CI having a first service conception rate of 47%. The variables that really determine the CI are days to first service and heat detection with heat detection having a strong influence of days to first service. Over the past 15 years heat detection rates have dropped 30 percent. At the same time milk production has gone up 25 percent and average herd size has increased 20 percent. Cows receive less individual attention, spend more time on concrete, and the effects are greater of negative energy balance created in early lactation when cows do not consume enough dry matter and/or energy to meet the nutrient needs required for higher milk yields. I believe these factors have worked together to depress the expression of estrus and thus make heat detection more difficult with extended days to first service and lower heat detection efficiency .

Table 1. Change in daily milk yield, days in milk, 305 day ME milk, and reproductive performance for Holstein herds (n=4771) processed by DRMS and stratified by calving interval1.

Calving Interval (months)
Item	<13	13 to 13.9	14 to 14.9	15 to 15.9	16 to 16.9	>16.9
Number of herds	129	1416	1856	919	290	161
Average herd size	83	159	160	157	125	165
Daily milk yield (lbs)	66.5	67.1	64.2	60.3	57.3	53.5
Days to 1st service	74	82	93	105	120	140
Conception rate 1st service	47	41	40	40	42	47
% heat observed	53	50	44	38	33	26
Projected 305 day ME milk (lbs)	22,751	23,652	23,264	22,404	21,592	20,791
1 DairyMetrics reports were generated on September 11, 2002 using current DHI information for Holstein herds that have a twice daily milking schedule and 25% or less of the services were to non-AI sires.

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