New activity-based fertility traits for Norwegian Red dairy cattle : definitions, heritabilities and comparison to traditional fertility traits
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The aim of this study was to define and calculate heritabilities for new activity-based fertility traits for Norwegian Red (NRF) dairy cattle. The traits were time from calving to first high activity episode (CFHA), first estrus in heifers (FEH), estrus duration (ED) and estrus strength (ES). Time form calving to first insemination (CFI) is a fertility trait already used in the NRF’s breeding scheme and are included in the study for comparison to the new traits. Relative activity change was measured with Heatime RuminAct (SCR, Netanya, Israel), where activity measured in a 2-hour interval is compared to the normal activity levels for each individual animal based on records from the previous week. A high activity episode is interpreted to be an indicator of estrus and was registered with at least three continuous recordings above threshold value and ended with two continuous recordings under threshold. A total of 1104 NRF from 33 free stall herds in Norway wore activity units. CFI was calculated based on the first parity from 2007 to 2018 for 3820 registered NRF cows from the 33 herds. A total of 573 NRF animals from 27 herds had activity change data and were successfully linked to data from the Norwegian Dairy Herd Recording System. After editing, only 117 cows met the requirements for CFHA recording, 101 for FEH and 491 for ED and ES. Least square means showed a difference in expression of fertility traits for different seasons and parities. Autumn gave the best expressions, while parity one showed the weakest signs. Of the significant phenotypic correlations, it was a favourable correlation between ED and ES and unfavourable between CFHA and ES. Estimated heritabilities for the new activity-based traits were low (0.00-0.05) with large standard errors. Estimated heritability for CFI was 0.02 with a standard error of 0.02. There are some challenges with using a herd management tool like Heatime RuminAct to register phenotypes for breeding purposes. First, most recordings started too late to register CFHA and FEH. Secondly, activity registrations must be continuous, without lack of recordings. Third, too few recording units on the farm will lead to pre-selection since there is no point recording activity of an animal that will not be inseminated. Fourth, proper identification of the animal using an activity unit is a must. Consequently, this study has shown that recommendations for use is necessary if herd management tools are to be used for data collection for breeding purposes. The use of activity measurements is promising with enough data material.Målet med oppgaven var å definere, samt estimere arvegrader, til nye fertilitetsegenskaper til norsk rødt fe (NRF) basert på aktivitetsmålinger. Egenskapene var tid fra kalving til første aktivitetsøkning (CFHA), første brust hos kviger (FEH), brunst lengde (ED) og brunst styrke (ES). Til sammenligning, er tid fra kalving til først inseminering (CFI) inkludert i oppgaven siden egenskapen inngår i det nåværende avlsprogrammet til NRF.