Sunday, September 25, 2016

Goats Faced Huge Parasite Challenge

The primary goal of the Western Maryland Pasture-Based Meat Goat Test is to identify meat goat bucklings that are resistant and resilient to gastro-intestinal parasites. Parasite resistance is quantified by fecal egg counts:  eggs per gram of feces (EPG). It is assumed that a higher egg count equates to more worms in the animal's gut. Adult worms lay eggs and suck blood, whereas immature worms only suck blood.

Upon arrival, fecal egg counts ranged from 0 to 21150 epg and averaged 1070 ±  3024 epg. The standard deviation was almost three times the mean, indicating a very wide variation in starting egg counts. In fact, the median FEC was only 100 epg. If the two egg counts that were above 10000 epg are removed from the data set, the mean is reduced to 652 ± 1314 epg.

Fecal egg counts doubled by day 42 (2349 ± 2006 epg, median 1988 epg) and began to get dangerously high by day 56 (4584 ± 3844, median 3750 epg). By day 70, the average fecal egg count had risen to 5739 ± 5937 epg (median, 4233 epg).  The barber pole worm is a prolific egg-layer. 2000 epg is often considered to be of clinical significance. Egg counts above 5000 epg are considered very high and losses can be expected.

In the test, bucks whose average egg counts are below 1000 epg and highest egg counts are below 2000 epg are considered to be resistant. This year, five bucks met this criteria:  616 (Davis, MO), 648 (Murphy, NJ), 661 (Peters, NC), 687 (Weber, IL), and 699 (Yutzy, OH). The most resistant buck in the test is 661. His fecal egg count averaged 364 epg. His highest fecal egg count was only 920 epg.

A maximum of five fecal egg counts was used to evaluate the bucks for parasite resistance. The incoming FEC (June 23-24) was not factored into test results because it would have been the result of past management practices and not necessarily genetics. The next fecal egg count (July 8) was also not factored into test results because it was affected by the initial dewormings with Valbazen®, Cydectin®, and Prohibit®.

Many things confounded the analysis of fecal egg count data and identification of resistant bucks.  If a goat required deworming, his next fecal egg count (14 days  later) was not factored into test results, as it would have been affected (hopefully reduced) by the treatment. In the summary report, the fecal egg counts that follow dewormings are in red text. It is not always possible to obtain a fecal sample from a goat, especially if it has scours. If a goat doesn't have a fecal sample, it can't be disqualifying. Two attempts are made to obtain fecal samples from the goats. Resistance to all the drugs is another confounding factor. Fortunately, the initial dewormings were largely effective at reducing fecal egg counts in the goats that came in with high loads.

It goes without saying that this year's test bucks faced a very serious parasite challenge. This has been the situation for the past several years, but this year, the challenge was especially high. The five most resistant bucks in this year's test should be highly valued.

Special thanks to Dr. Dahlia O'Brien at Virginia State University for doing all the fecal egg counts and larvae ID. She has supported the test for many years and we couldn't do it without her.

Download fecal egg count summary