Evaluating the relationship between fecal egg count, FAMACHA score, and weight in dewormed and non-dewormed Katahdin rams during a parasite challenge

Abstract

The objective of this study was to evaluate and to estimate the relationship between fecal egg counts (FEC) and FAMACHA© score and the body weight of growing Katahdin rams during a parasite challenge. One of the largest factors negatively influencing reproduction and economics in the sheep industry is gastrointestinal nematode (GIN) parasites. Due to anthelmintic resistance of these parasites, animals are selected for parasite resistance using FEC and FAMACHA© scores. Data were used from the Virginia Tech Southwest Agricultural Research and Extension Center Ram Test in Glade Spring, VA from the years 2012 to 2018 in which animals were tested in 14-day intervals for 70 days. Mixed models for repeated weight measurements were made from backwards stepwise selection to evaluate relationships between weight and GIN FEC. A total of 576 animals within 23 contemporary groups derived from test year and pasture group were analyzed. Ram, contemporary group, and consignor were considered random effects, and fixed effects were birth type, test day, age, age squared, starting weight, FEC, and FAMACHA© score. Pairwise contrasts were used in the statistical analysis of parameters and their interactions. Weight and age were found to have a quadratic relationship. Increased FEC was associated with weight loss at a rate of 0.00030 kg/FEC (P < 0.0001). Animals dewormed at any point during the trial weighed less than those that were not and increased with test day to a maximum difference of 4.66 kg (P < 0.001). FAMACHA© score was found to be significant (P < 0.05), but a direct relationship with weight was not conclusive. Overall, rams with severe enough parasite load to require deworming had lesser weights, which could impact profitability of sheep production and reinforced the need to select animals that had greater innate parasite resistance.

Genomic Regions Associated with Resistance to Gastrointestinal Nematode Parasites in Sheep—A Review

“…3 H. contortus resistance, as defined by reference [40], is a phenotype measuring fecal egg count after artificial challenge with H. contortus, used to identify regions under selection for resistance to gastrointestinal nematodes. 4 H. contortus resistance, as defined by reference [38], is a phenotype obtained after ranking animals as extremely resistant or susceptible based on combined measurements of FEC, PCV, and live weight. 5 Resistance to GINs refers to the average of four replicates of fecal egg count that were collected at approximately 16, 20, and 24 weeks of age; however, the specific age at the time of sampling associated with the region was not specified by the authors.…”

“…[3]. Nematodes infect the small intestine and abomasum of grazing sheep, and animals can develop detrimental symptoms such as weight loss, diarrhea, hypoproteinemia, and anemia [3][4][5] and can die of infection if left untreated [6]. GIN infection is an animal welfare issue, and producers can face substantial economic losses that are difficult to measure.…”

Practical guide to the diagnostics of ruminant gastrointestinal nematodes, liver fluke and lungworm infection: interpretation and usability of results

“…However, there are questions regarding its impact on productivity. Most published research on this topic indicates no negative effect [51][52][53][54], but authors have pointed to potential losses [46,55], mainly when FAMACHA© is used in lambs [56,57]. The FAMACHA ® system is considered to be one of the best TST criteria in ewes [51,52,58].…”

“…However, even when Haemonchus is the major parasite, it is not recommended to use the FAMACHA ® system as an exclusive criterion for TST in growing lambs. The productive criterion of weight gain in lambs can be effectively used in TST for the control of GIN without productive losses, regardless of any association with the FAMACHA ® system [55,56]. Additionally, it is known that the presence of Fasciola and/or Eimeria can compromise the success of FAMACHA ® implementation [59].…”

Genetic parameters for resistance to gastrointestinal nematodes in sheep: a meta-analysis

“…Resistance to GIN is a desirable trait to breed for because higher resistance (e.g. lower FEC) is often associated with improved animal performance (Cruz-Rojo et al, 2012; Fthenakis et al, 2015; Galyon et al, 2020; Idika et al, 2012; Mavrot et al, 2015; Notter et al, 2017). As such, it may be expected that breeding for increased resistance should also lead to improved performance.…”