Effect of Herd Size on Year 2000 DHIA Summaries

Dr. Allen Young
USU Extension Dairy Specialist

For the last several years, I have been putting together management reports for Rocky Mountain DHIA’s Annual Summary. In addition to summaries based on production, we include reports summarized by herd size. Herd size has been suggested as a factor for many production traits. In this article I am including a small selection of the total production parameters that we looked at because I think it can be instructive.

The selection criteria for herds that were included in the reports are given below. These criteria excluded about 75 out of 353 herds from consideration in the averages.

Criteria: Milk per cow increased as herd size increased in Holstein herds up to 500 cows, then decreased in herds of over 500 cows (Table 1). This trend is similar to last year, except that this year’s production is higher per cow than last year’s. Milk production in Jersey herds did not seem to be related to herd size; however, the smaller herds increased production this year compared with last year (Table 2).

The average % Low Somatic Cell Count (SCC) (0 - 4 linear score) is the percentage of your herd which has a linear score of under 4.5 or 283,000 SCC. The thing to keep in mind is that you want the average % Low SCC number to be higher if you want to have better herd udder health (i.e., less mastitis). My “rule-of-thumb” is 90% or greater in the average % low SCC category signifies a herd with excellent udder health. In Holstein herds, herd size does not appear to be a major factor in determining the level of this category (i.e., larger herds are not necessarily better or worse than smaller herds); however, increased herd size for Jerseys tended to correlate with improved udder health. Percent of cows with low SCC has stayed about the same over the last 10 years at 80%. This number needs to be higher.

Days in Milk at 1st Breeding for Holstein herds decreased as herd size increased, yet average Days Open was not different until an increase occurred for the 500+ cow herd size. This suggests that larger herds are maintaining the same level of reproduction by starting breeding sooner than smaller herds. As herd size increased for Jersey herds, Services per Conception decreased, yet Days Open showed no specific trend. The dairies in the largest Jersey herd size category waited longer to start breeding, but did a better job once they started.

For several years we have been suggesting that heifers should calve for the first time at around 24 months of age. Over the past 10 years, average age at calving has decreased from 27.3 months to 26 months. This is moving in the right direction, but we aren’t progressing fast enough! As shown in Tables 1 and 2, only Holstein herds of 500+ and Jersey herds over 50 cows had an average Age at First Calving below 26 months, suggesting that larger herds do a better job of heifer raising. Compared with last year, neither Jersey herds or Holstein herds showed any improvement. The herd size trend was similar in both years.

These are only a few of several parameters that I looked at. For further information and to get last year’s reports, you can look on the USU Dairy Extension Web site at: http://extension.usu.edu/coop/ag//livestoc/dairy/
Click on USU Dairy Research and Continuing Education, then DHIA Management Reports.

This year’s reports will be added in the near future. If there is a relationship that you would like me to compute, drop me a line. I would love to hear from you.


Table 1. Selected Management Parameters, by Herd Size, for Rocky Mountain DHIA Affiliate Holstein Herds. >
Herd Size No. Herds No. Cows Ave. Milk/Cow Avg. %
Low SCC
(0-4 LS)		 Days First Breed Serv. Per Conc. Days Open Calving Interval Avg. Age First Calving
less than 75 48 2,732 19,582 80.5 103.8 2.10 162 14.6 28.3
75-150 87 10,057 21,425 82.5 97.7 2.09 156 14.2 27.7
150-300 68 15,207 22,732 81.6 98.0 2.16 163 14.3 27.4
300-500 30 12,092 25,015 80.3 91.7 2.26 160 14.2 26.7
500+ 21 18,503 23,875 80.9 89.9 2.38 168 14.1 25.0
TOTAL 254 58,591 22,053 81.5 97.6 2.16 161 14.3 27.4


Table 2. Selected Management Parameters, by Herd Size, for Rocky Mountain DHIA Affiliate Jersey Herds. >
HERD SIZE No. Herds No. Cows Ave. Milk/Cow Avg. % Low SCC (0-4 LS) Days First Breed Serv. Per Conc. Days Open Calving Interval Avg. Age First Calving
less than 50 6 178 15,931 76.0 67.8 2.73 156 13.4 27.6
50-100 6 482 15,415 78.7 80.2 2.03 131 14.1 24.7
100+ 12 2,113 15,755 80.5 91.6 1.85 146 13.7 25.1
TOTAL 24 2,773 15,714 78.9 82.8 2.11 145 13.7 25.5