Relationship of udder morphology with milk yield and mammary gland health of alpine goats

Kao rezultat dugogodišnje selekcije visokomliječnih koza radi povećanja proizvodnje mlijeka, sve je zamjetnije narušavanje morfologije njihova vimena, što nerijetko rezultira narušenim muznim odlikama koza s posljedičnom upalom vimena, odnosno smanjenjem proizvodnje i promijenjenim kemijskim sastavom mlijeka. Cilj istraživanja bio je, stoga, utvrditi međupovezanost morfologije vimena, proizvodnje i kemijskog sastava mlijeka te zdravlja vimena alpina koza, kao nazastupljenije mliječne pasmine koza u Hrvatskoj. Istraživanjem je bilo obuhvaćeno 139 strojno muzenih i zdravih (bez uočenih znakova kliničkog mastitisa) alpina koza, držanih u istom stadu (slobodnom od artritis encefalitisa) i podređenih identičnoj tehnologiji uzgoja/proizvodnje. Tijekom istraživane laktacije (od odbića do zasušenja) u navedenom su stadu provedene kontrole mliječnosti (AT4 metoda) i redovita mjesečna prikupljanja pojedinačnih uzoraka mlijeka radi utvrđivanja njihova kemijskog sastava. Od svake su koze pri prvoj, četvrtoj i sedmoj kontroli mliječnosti uzeta po dva uzorka mlijeka (po jedan iz lijeve, odnosno desne polovice vimena) radi određivanja broja somatskih stanica (BSS), odnosno po dva uzorka u svrhu mikrobiološke pretrage mlijeka te su vizualnom prosudbom i mjerenjem utvrđene morfološke odlike vimena istraživanih koza. Utvrđeno je postojanje dvaju (podjednako zastupljenih) oblika vimena, i to: kruškolik (51,8% istraživanih koza) i ovalan oblik vimena (48,2% koza). U većine (56%) koza utvrđeno je postojanje sisa ljevkastog oblika, dok je sise cilindričnog oblika imalo 28%, a sise oblika boce 16% istraživanih koza. Prosječni opseg vimena alpina koza bio je 51,19 cm, širina vimena 13,67 cm, dubina vimena 18,85 cm, udaljenost između vrhova sisa 10,95 cm, kut sisa 39,15, duljina sisa 5,45 i širina sisa 3,45 cm. Utvrđen je značajan utjecaj redoslijeda i stadija laktacije i broja ojarene jaradi u leglu na većinu analiziranih morfoloških odlika vimena, dok su dubina i širina vimena te veličina sisa bile pozitivno povezane s utvrđenim pokazateljima tjelesne razvijenosti koza (dubina prsa, obujam prsiju i tjelesna masa). Istraživane koze su tijekom prosječnog trajanja laktacije od 294,7 dana proizvele 898,9 kg mlijeka, odnosno prosječno dnevno 2,98 kg mlijeka Istraživanjem nisu utvrđene značajne razlike u proizvodnji i prosječnom kemijskom sastavu mlijeka između koza različitih oblika vimena. Najviše mlijeka su proizvele koze sa sisama u obliku boce, odnosno značajno više nego koze sa ljevkastim sisama. Pritom su sise oblika boce bile značajno veće te postavljene horizontalnije i s većom udaljenošću jedna od druge u odnosu na sise drugačijih oblika. Utvrđena je značajna linearna regresija između većine utvđenih mjera vimena (P<0,001) i sisa (P<0,05) i laktacijske proizvodnje mlijeka, dok su najznačajniji pokazatelji miječnosti koza bili opseg, dubina i širina vimena (R2=0,23-0,35). Značajno veća (P<0,05) učestalost intramamarnih infekcija je dijagnosticirana u jedinki ovalnog oblika vimena nego u jedinki tzv. kruškolikog oblika vimena (17,9:12,5%), a ujedno i veći (P<0,05) geometrijski prosjek BSS (663x103 : 482x103/mL). Utvrđene su značajne (P<0,05) razlike u BSS, kao i u učestalosti intramamarnih infekcija (P<0,05) s obzirom na utvrđeni oblik sisa, pri čemu je u koza sa sisama u obliku boce utvrđena najveća učestalost intramamarnih infekcija, kao i najveći BSS u mlijeku. Većina morfoloških odlika vimena bila je u značajnoj korelaciji s BSS te je s povećanjem dubine vimena i veličine sisa, kao i smanjenjem kuta sisa i udaljenosti između vrhova sisa utvrđeno smanjenje BSS, što se može povezati i sa smanjenjem udaljenosti sisa od tla. Duljina sisa bila je statistički najznačajniji procjenitelj (P=0,0548) nastanka infekcije mliječne žlijezde, a najveća učestalost intramamarnih infekcija je uočena u koza sa najdužim sisama (>6,5 cm), dok je (u pogledu zdravlja vimena) najoptimalnija duljina sisa 5,5 - 6 cm. Istraživanjem dobivene spoznaje mogu doprinijeti uvođenju morfologije vimena u provedbu uzgojnih programa za alpina koze u cilju daljnjeg povećanja mliječnosti, ali bez nužno negativnog odražavanja na zdravlje njihova vimena.In herds of high-producing dairy goats, as a result of long-term selection to increase milk yield, a deterioration in udder morphology is increasingly noticeable (e.g. large and drooping udders, horizontally placed teats, large teats unsuitable for machine milking, teats close to the ground, etc.), which not only affects milking characteristics, but also has a negative impact on udder health. Namely, it is known that mastitis is the most common and at the same time the most expensive disease in dairy goat herds, i.e. an important factor for the production longevity of dairy goats. Related to this, in recent scientific literature, certain morphological characteristics of goat udders and teats are increasingly cited as factors for premature excretion, especially in high-producing genotypes. Considering that goat milk production in Croatia is based on high-producing breeds, the most numerous of which is Alpine, the aim of the study was to confirm the hypothesis of the connection of udder morphology with milk production and chemical composition, i.e. the association of certain udder morphological characteristics with indicators of mammary gland health in Alpine goats. The study included 139 purebred and machine milked Alpine goats of different lactation orders. The selected livestock units had symmetrically developed udders with no visible signs of mastitis. The same breeding and production technology (feeding, housing, method and number of daily milkings, etc.) was applied in the studied livestock units kept in the same herd. Goats were kept indoors throughout the year, which allowed the monitoring of individual livestock units, especially with regard to the occurrence of possible diseases or the monitoring of individual reproductive phases. During the milking period, regular monthly milking controls of goats were carried out using the AT4 method, by which also individual milk samples were collected to determine chemical composition. The morphological characteristics of the udder were determined (assessments of the goat’s udder and teats according to the shape and measurement of the morphological characteristics) once in the early, middle, and late stages of lactation. Also, during the aforementioned milking controls, one milk sample was taken from each half of the udder for microbiological tests and determination of somatic cell count (SCC). Statistical analysis was performed using SAS V 9.4 software package (SAS STAT, 2013). The presence of two udder types was found in Alpine goats: the pear-shaped udder, characteristic of highproducing goats, was found in 51.8% of Alpine goats, and the oval shape in 48.2%. The average udder circumference was 51.19 cm, width 13.67 cm, and depth 18.85 cm. Majority (56%) of the goats surveyed had funnel-shaped teats. 28.1% of the goats had cylindrical teats, while 16% of the goats had teats with the so-called bottle-shaped tip. On average, the bottle-shaped teats were largest in terms of length and width, and also the most vertical (the smallest average teat angle) compared to the other two teat types. The morphological characteristics of the udder increased with the progress of lactation. In addition, significantly larger circumference and depth of the udder and length and width of the teats were observed in goats with a larger litter compared to goats with one kid in the litter. In terms of chemical composition of milk, the milk of goats in the first lactation and in the earlier stages of lactation was the richest in terms of dry matter content, dry matter without fat, milk fat, and protein content. Higher proportions of chemical indicators were also found in the milk of goats with one kid, which is a consequence of less frequent udder emptying and lower level of production of the total amount of milk. The content of all analysed ingredients, except lactose, was lower with higher daily and lactation milk production. The highest SCC in the middle stage of lactation was found in healthy goats. While udder shape had no effect on average milk production, chemical composition, and duration of lactation, a significant positive correlation was found between other morphological characteristics of the udder and milk production and SCC. Goats with the most developed udder, bottle-shaped teats, and larger dimensions achieved the highest average daily and lactation milk production, and longer and wider breasts and an oval shape of the udder were associated with higher SCC and higher prevalence of subclinical udder inflammation. A higher prevalence of subclinical mastitis was found in goats with one kid than in goats with more kids. The results of this study indicate the importance of udder morphology as a factor in udder health, chemical composition, and milk production. Knowledge of morphological traits can contribute to the development of a separate breeding program for the Alpine goat, with the aim of genetically improving of udder morphology to increase milk yield