Genetic parameters for the external udder morphology in commercial farms of Istrian sheep from Croatia

Short communication Journal of Central European Agriculture, 2019, 20(1), p.68-73 DOI: /10.5513/JCEA01/20.1.2462 Genetic parameters for the external udder morphology in commercial farms of Istrian sheep from Croatia Dragica ŠALAMON*, Petra FURDIĆ, Toni TEŠIJA and Alen DŽIDIĆ Faculty of Agriculture, University of Zagreb, Department of animal science, Svetošimunska cesta 25, 10000 Zagreb, *correspondence: Abstract Istrian sheep is a local breed with superior milk yield and composition. Excellent udder shape of this breed needs to be preserved in future, since it’s economic value resides within the artisanal cheese production. Genetic parameters for the teat angle (Alpha) and the height of the cisternal part below the teat orifice (Cis) were estimated in order to evaluate the possibility for conservation of udder traits amiable for machine milking. Udder morphometry of the 240 registered Istrian ewes was measured from digital photographs of the posterior view of the udder on 10 commercial farms three times during lactation. Original pedigree records were trimmed to four recent generations. Heritabilities were estimated using single trait animal model. The stage of the lactation, interaction of lactation number, month of lambing and the farm were fixed effects, and the additive genetic value of the individual and permanent environment of the individual were random effects. Estimated heritability was 0.05 for Alpha and 0.71 for Cis mid-lactation measurements. Measurements of Cis during lactation did not result in a significant additive effect. The result shows potential in estimating genetic parameters of important udder traits in small commercial dairy ewe populations, using the digital mesurements, given the reduction of non-genetic variability in the sample. Keywords: animal model, digital morphometry, genetic parameters, udder shape Introduction Istrian sheep is the second smallest autochthonous sheep population in Croatia with 2,515 animals registered on 38 farms, and makes for 5% of the total number of sheep of an approved selection program of the Croatian Agricultural Agency. Predominately semi-extensive farms have average herd size of 55 animals. Milk is processed into hard artisanal cheese and curd on small family cheese dairies, or sold for industrial cheese production. Machine milking is present in Istrian sheep, while the other local breeds in Croatia are predominately milked by hand. The aptitude of the Istrian sheep for machine milking is evaluated positively: small angle that teat closes with the vertical axis of the udder (Alpha), small cisternal height below the teat orifice (Cis), and satisfactory milk flow kinetics (Šalamon and Džidić, 2014). 68 Short communication DOI: /10.5513/JCEA01/20.1.2462 Salamon et al.: Genetic parameters for the external udder morphology in commercial farms of... Improved udder traits in the selection objectives of ovine breeding schemes were implemented on the experimental intensive farms in the Mediterranean (De La Fuente et al., 1996; Marie-Etancelin et al., 2005; Casu et al., 2006) because of the “baggy udders” of the ewes selected for high milk yield. The cisternal part of the udder below the teat orifice is enlarged in such udders, as is the angle between the teat and the vertical axis of the udder (Fernandez et al., 1997; Marie-Etancelin et al., 2005). Milking of the “baggy udders” is not efficient because part of the cisternal milk remains below the teat orifice unless the milker applies manual manipulation of the udder during stripping (Bruckmaier et al., 1997). Additionally, horizontally implanted teats cannot hold the weight of the milking unit, which then tends to fall off. With milking already being the most time-demanding procedure on ewe dairy farms, this additional manipulation prolongs the total milking time of the herd. Dry milking can appear, injuring the teat tissue and the udder (Fernandez et al., 1997; Bergonier et al., 2003; Legarra and Ugarte, 2005). Udder traits as selection goals for sheep are not common outside experimental farms due to the recording cost. Besides the onfarm measuring of the udder at experimental farms, successful appraisal method based on 9-point linear scale has been applied in production herds of the Churra breed, proposed by De La Fuente et al. (1996) and adapted for other dairy breeds (Fernandez et al., 1997; Legara and Ugarte, 2005; Marie-Etancelin et al., 2005; Casu et al., 2006). To lessen the cost of the trained technicians, the use of digital photographs of the udder for digital measuring was proposed by Dzidic et al. (2009). The aim of this study was to evaluate the possibility for conservation of udder traits amiable for machine milking by estimating the genetic parameters for the teat angle (Alpha) and the height of the cisternal part below the teat orifice (Cis) using the digital measurements of the udder. Materials and methods Six of the sampled commercial farms performed milking by hand and five used machine milking. Digital photographs of 750 ewe’s posterior view of the udder were taken prior to evening milking three times during the lactation: early (days 8 to 95), mid- (between days 96 and 135) and late lactation measurements (days 96 to 135 of lactation). Cis and Alpha were measured from the digital photographs as described in Šalamon and Džidić (2014). Total of 1,397 records were edited removing non-logical values, animals without ID information or without information on the beginning of lactation, and animals with less than two records. Values 1.5 interquartile range lower than the first and higher than the third quartile were removed. Mixed model including all of the fixed effects used later in the animal model was used to remove all records having RStudent by leverage estimation of residuals higher than 2 or lower than -2. Description of the 140 ewes’ data from 10 farms clustered in three groups due to small number of observations, and of the average lactation stage 1.94 (lactations 6 and higher were pooled in one common cluster) is shown in Table 1. Pedigree records obtained from the Croatian agricultural agency (24,219), were cleaned (9% non-logical) and trimmed the last four generations, shown in Table 2. 69 Short communication DOI: /10.5513/JCEA01/20.1.2462 Salamon et al.: Genetic parameters for the external udder morphology in commercial farms of... Table 1. Descriptive statistics for Cis and Alpha measurements N (N1, N2, N3) Lact. Min-Max Mean SD SE Cis 862 (286, 342, 234) 3.14 0-3.7 1.26 0.69 0.02 Alpha 848 (281, 338, 229) 3.2 3.5-71.9 37.61 13.31 0.46 Alpha - the teat angle (o); Cis - the height of the cisternal part below the teat orifice (cm); N (N1, N2, N3) – number of observations (number of early lactation, of mid-lactation, and of late lactation observations); Lact. – Average number of lactation; Min-Max – minimal and maximal observation; SD – standard deviation; SE – standard error. Table 2. Characteristics of th (...truncated)