Fecal egg counts and individual milk production in temperate pastoral dairy systems of Australia

Abstract

Anthelmintic use in lactating dairy cattle has been shown to result in a milk production response in some previous studies. If individual animals within a herd could be identified that would most benefit from anthelmintic treatment, this may reduce anthelmintic resistance. Australian dairy systems are predominantly pasture based, allowing sustained exposure and immune stimulation of cattle to gastrointestinal nematodes. We assessed the relationship between milk production and early-lactation fecal egg counts (FEC) to determine whether cows with higher FEC produced less milk. Ten pasture-based dairy farms in south-west Victoria, Australia, entered an observational study. Individual FEC at a minimum detectable count of 2.5 eggs per gram of feces (epg) were recorded for recently calved primiparous and multiparous cohorts on each farm. All animals were calved ≤30 d at sampling. Body condition scores were assessed at sampling and milk production data were collected from daily milk meters and herd tests to give first 100-d milk production. When separated by primiparous or multiparous status, no difference in the milk production between cows with FEC = 0 and FEC ≥2.5 epg was identified. Between-farm variation was large for FEC and milk production. Fecal egg count at a minimum detectable count of 2.5 epg detected parasitism in primiparous cows postcalving, but the presence and magnitude of parasitism measurable by FEC was not related to milk production in pasture-based Australian dairy systems. In multiparous cows, the rate detection of worm eggs at this analytical sensitivity was lower and the significance of a positive FEC at this analytical sensitivity requires further assessment to ascertain the effect on milk production. Based on our study, it seems unlikely that individual FEC results would be useful as a basis to select individual cows in south-west Victorian dairy herds for anthelmintic treatment.

Summary: Pasture-based dairy cows were assessed for postpartum fecal egg count (FEC) and 100-day milk production. No relationship was observed between milk production and cows with positive and negative FEC at an analytical FEC sensitivity of 2.5 eggs per gram (epg).

Figure 1

Fecal egg counts with relationship to production quartile for primiparous cows (A) and multiparous cows (B). Individual cows were ranked against their peers within parity and farm groups and assigned to a production quartile; these quartiles were assessed for distribution of FEC. Quartile 4 represented the highest 25% of individual milk yields on each farm.

Figure 2

Milk production in cows with a FEC ≥2.5 epg postcalving compared with their peers of FEC = 0 for primiparous cows (A) and multiparous cows (B). Only includes farms where ≥30% of cohort had a positive FEC. Boxplots illustrate the median and interquartile ranges for each group on the farms. The whiskers illustrate the upper and lower quartile ranges with the exception of outliers. Outliers are represented by dots in some plots.