| Sažetak | Utjecaj dobi prvog pripusta na proizvodne pokazatelje je nedovoljno istražen kod koza, a rezultati dosadašnjih istraživanja koji se dotiču ove problematike, nisu dovoljno informativni i dostatni za donošenje zaključaka. Kako bi se dobio što objektivniji odgovor na pitanje „kako dob prvog pripusta utječe na cjeloživotnu proizvodnju mlijeka i jaradi u intenzivnim sustavima proizvodnje mlijeka?“, cilj ovog istraživanja bio je utvrditi u kojoj mjeri dob prvog pripusta utječe na 1) duljinu laktacije (period mužnje); 2) količinu proizvedenog mlijeka, mliječne masti, bjelančevina i laktoze; 3) udio mliječne masti, bjelančevina i laktoze; 4) broj somatskih stanica u mlijeku, 5) broj jaradi u leglu, 6) porodnu masu jaradi i 7) ukupnu masu legla. Pritom su, ovisno o svojstvu, korišteni svi dostupni izvori fenotipske varijabilnosti pomoću odgovarajućih statističkih modela. Istraživanje je provedeno na populaciji uzgojno valjanih koza pasmine alpina (n=12 769) koristeći ukupno 41 645 zapisa za svako analizirano svojstvo. Proizvodnost koza je provođena u skladu sa uputama ICAR – a. Analiza cjeloživotne proizvodnje povedena je na ukupno 9 857 koza i isto toliko fenotipskih zapisa za svako svojstvo (razlika u broju koza u ta dva dijela istraživanja proizlazi iz nepoznatog datuma izlučivanja nekih koza iz proizvodnje, a i činjenice da neke koze u trenutku provedbe istraživanja još nisu bile izlučene). U razdoblju od 235 dana mužnje, koze su prosječno dnevno proizvele 2,5 kg mlijeka sa 3,4 % mliječne masti, 3 % bjelančevina, 4,2 % laktoze i 558 tisuća somatskih stanica (u mL mlijeka). Prosječna veličina legla je bila 1,26 jaradi, individualna porodna masa 3,22 kg, a masa legla 4,12 kg. Prosječni životni vijek koza bio je 70 mjeseci i pritom su prosječno proizvele 1925 kg mlijeka, 64 kg mliječne masti, 58 kg bjelančevina, 81 kg laktoze i 4 jaradi. Dob prvog pripusta u istraživanoj populaciji bila je u rasponu od 5 do 25 mjeseci (prosjek 9). Regresijom fenotipskih podataka na dob prvog pripusta ANCOVA statističkim modelom s ponovljenim mjerenjima utvrđen je smjer i intenzitet utjecaja dobi prvog pripusta na 1) duljinu laktacije, 2) količinu proizvedenog mlijeka, mliječne masti, bjelančevina i laktoze u laktaciji, 3) udio (%) mliječne masti, bjelančevina i laktoze u mlijeku, 4) broj somatskih stanica, 5) veličinu legla, 6) porodnu masu i 7) ukupnu masu legla. Uz manje komparativne razlike, može se zaključiti da je dob prvog pripusta u prvih nekoliko laktacija/jarenja imala pozitivan, a u poznim laktacijama negativan utjecaj na većinu istraživanih svojstava. Izuzetak su bili: udjeli mliječne masti, bjelančevina i laktoze u mlijeku, kod kojih je u pravilu utvrđen obrnuti slijed promjena; te broj somatskih stanica, kod kojih je dob prvog pripusta kroz sve laktacije pozitivno korelirala sa brojem somatskih stanica. Valja napomenuti da su različite skupine svojstava analizirane na jednoj te istoj populaciji, što znatno doprinosi kreiranju potpunije slike kako se istraživani utjecaj odražava na reprodukcijsku i proizvodnu učinkovitost koza. Regresirajući cjeloživotnu proizvodnju pokazatelja mliječnosti i reprodukcije na dob prvog pripusta u okviru ANCOVA analize, procijenjeno je da se prolongiranjem prvog pripusta za godinu dana očekuje skoro jedna laktacija manje (0,72 laktacije), a posljedično tome i gubitci od 0,84 jareta, 336,48 kg mlijeka, 10,92 kg mliječne masti, 10,08 kg bjelančevina, 14,04 kg laktoze. Rezultati regresijskih analiza po rednom broju laktacije (jarenja) uz rezultate koji se odnose na cjeloživotnu proizvodnju (kumulativ individualnih laktacija), zajednički pridonose potpunijem shvaćanju promjena u proizvodnji koje su uvjetovane različitom dobi prvog pripusta (osjemenjivanja). Procijenjeni parametri provedenih regresijskih analiza upućuju na zaključak koji je donekle suprotan dosadašnjim prevalentnim stavovima struke i uzgajivača, utemeljenim na negativnim učincima ranijeg pripusta na proizvodnju u ranijoj životnoj dobi. Naime, predmetno istraživanje rezultiralo je dostatnim brojem znanstveno utemeljenih dokaza da se gubitci u ranijim fazama proizvodnje, a uvjetovani ranijim pripustom, kompenziraju u kasnijim laktacijama, te kako se ranijim pripustom jarica ostvaruju dodatni doprinosi kroz veći broj laktacija u životnom vijeku. |
| Sažetak (engleski) | The impact of age at first mating (insemination) on production characteristics has not been sufficiently investigated in goats, and the results of previous research tackling this issue are insufficiently informative and conclusive. In order to get some scientifically underpinned clues about the impact of the first mating on the overall production of goats in intensive production systems, the study aimed to determine to what extent the age of the first mating affects 1) the length of lactation (milking period); 2) the milk yield, fat yield, protein yield and lactose yield in the milking period; 3) the fat content, protein content, and lactose content; 4) the somatic cells count, 5) the litter size, 6) the birth weight (individual) and 7) the total litter weight (joint weight of kids). In order to obtain as possible as accurate estimates of the targeted effect, all the available sources of phenotypic variability were used via appropriate statistical model (the effects in the model varied between the examined traits i.e. dependent variables). The study was conducted on a population of Alpine goats (n=12769) using a total of 41645 records for each analysed trait. These goats were subjected to the official recording system of dairy and reproductive traits in accordance with the ICAR guidelines. The analysis of lifetime production was carried out on a total of 9857 goats (the same was the number of phenotypic records for each trait since phenotype in this analysis represented a cumulative of the lactation records, number of kids, and birth weights of all kids in the lifetime of the goats). The discrepancy in the number of goats in the two parts of the study was because of the unknown elimination date of some goats, but also due to some non-culled goats at the time of the downloading data for the analysis. During the period of 235 days of milking, the goats produced 2.5 kg/day of milk on average. The contents of fat, protein, and lactose were 3.4%, 3%, and 4.2%, respectively, and the somatic cell count was 558 000/mL. The average litter size was 1.26 kids, individual birth weight 3.22 kg, and litter weight 4.12 kg. The average lifespan of goats was 70 months, and their average lifetime production was 1925 kg of milk, 64 kg of milk fat, 58 kg of protein, 81 kg of lactose and 4 kids. The age of first mating (insemination) in the researched population ranged from 5 to 25 months (average 9). By regressing the phenotypic data on the age of the first mating using the ANCOVA statistical approach, the impact of age of the first mating was determined on: 1) the length of lactation, 2) the yields of milk, fat, protein, and lactose, 3) the contents of milk fat, protein and lactose, 4) the number of somatic cells, 5) the litter size, 6) the birth weight and 7) the total birth litter weight. Despite some comparative differences in the direction and the magnitude of the effect between the traits, it can be concluded that the effect positively affected the most important traits in the first couple of lactations (parities), but negatively in the later ones. The exceptions were the dry matter components (content), i.e. the content of the fat, protein, and lactose (practically the opposite trend); and the somatic cells count (positively correlated with the magnitude of the effect throughout all lactation orders). It is worthwhile to emphasise here that different groups of traits in this study were analysed on the same population, which significantly contributes to better understanding of the impact of the age of first parity on the reproductive and production efficiency of the goats in the intensive, dairy orientated production system. By regressing the lifetime production of milk yield and reproduction indicators on the age of the first lactation within the framework of the ANCOVA analysis, it was estimated that by postponing first mating by one year (12 months), it is expected loss of almost one full lactation (0.72 lactations less), and consequently a loss of 0.84 kids, 336.48 kg of milk, 10.92 kg of milk fat, 10.08 kg of protein, and 14.04 kg of lactose. The regressions nested within lactations in the first part of the study, along with the regressions performed on the lifetime production (cumulative yields of the animals across the lactations), jointly contribute to a more complete understanding of production and reproduction capabilities of goats predetermined (affected) by the different age of first mating (insemination). The estimated parameters of the performed regression analysis jointly lead to conclusion somewhat contrary to the prevailing attitude of the breeders and some experts in livestock husbandry. Precisely, there is prevailing consideration that later first mattings lead to better performances of dairy animals, and such attitudes have been underpinned by the already known positive effect of age at first mating on production and reproduction in the first lactation(s). However, little attention has been paid so far to the direction and magnitude of the effect in later age and later lactations of the goats. This research provided a sufficient amount of scientifically based evidences that losses in the earlier stages of production affected by earlier mating (insemination) of maiden goats, are compensated in later lactations, and that earlier mating in life additionally contributes to the production through a greater total number of lactations in the productive lifetime of the goats. |
