| Dairy cattle will often sort out the total mixed ration(TMR)in favor of the smaller grain particles and against long forage particles.Sorting of TMR affect the nutrient intake and subsequently might have a negative effect on the health of the cow.To explore the feed sorting behavior on dairy farms,three experiments were conducted to investigate the effects of early feed exposure(EFE)to different feedstuffs on feed preference and sorting behavior of dairy calves.In Experiment 1,Sixty(60)newborn Holstein calves(30 males,30 females)were randomly assigned to 1 of 3 EFE treatments including Concentrate(CON,only concentrate),Hay(HAY,only hay)and Concentrate and Hay(COH,both concentrate and hay)from d 2 to 56.Calves were fed milk twice per day until weaning on d 56.At d 56,fifteen(15)male calves(5 per treatment)were harvested for forestomach weight and rumen morphological parameters.After weaning,all female calves were offered both concentrate and hay in different buckets from d 57 to 70 to allow them free choice between the two feedstuffs.Calves were then transferred to heifers’ barn,housed in pairs in a pen and fed TMR from d 71 to 196.Feed intake,rectal temperature and calf health scores were recorded daily from d 2 to 70.Upon transition to a TMR,dry matter intake was calculated by each pen in the last week of experiment(d 190 to 196).Feed sorting was analyzed using samples taken from fresh feed and orts based on the particle size.A particle separator with 3 screens producing long,medium,short,and fine particle fractions was used.Sorting for each of the fractions was calculated as the actual intake of each fraction expressed as a percentage of predicted intake;values>100%indicate sorting for,values<100%indicate sorting against.Through out the experiment,body weight and structural growth were recorded,blood and rumen fluid were sampled for determining glucose,and ruminal pH and volatile fatty acids(VFA)concentrations,respectively.Early feed exposure did not significantly affect the performance and health of calves before and after weaning,but did affect the feed preference and rumen fermentation.After transition to a free-choice diet,HAY calves consumed more hay than CON(550.2 g vs.177.4 g,P<0.001),but this effect lasted for only a day.Provision of both concentrate and hay as separate components early in life resulted in a higher ratio of hay to total solid(35.6%)than provision of either concentrate(17.7%vs.35.6%,P = 0.03)or hay(16.5%vs.35.6%,P = 0.02),giving rise to a numerically higher rumen pH and lower VFA and blood glucose after weaning(during d 57 to 70).Upon transition to a TMR,a similar sorting pattern was exhibited,sorting against the long particle(98.0%)and for the fine particle fractions(104.1%).In order to gain a deeper understanding of how EFE affects sorting behavior of dairy calves once fed TMR immediately after weaning(week 8),experiment 2 was conducted with twenty newborn Holstein female calves,they were randomly assigned to a concentrate(CON)or hay(HAY).Feeding procedure was consistent with experiment 1 before weaning.After weaning,a novel TMR was supplied from week 9 to week 28.Calves previously exposed to hay sorted for more long particles and less fine particles than calves previously exposed to concentrate at week 9(122.0%vs.107.1%;P = 0.003;88.9%vs.95.0%,P = 0.01)and week 10(113.5%vs.102.4%,P = 0.007;92.6%vs.95.6%,P =0.02),respectively.However,after 18 weeks of exposure to the total mixed ration(week 28),sorting pattern was similar between CON and HAY.According to the results of experiment 1,which found that calves early exposed to both concentrate and hay as separate components had a greater intake of hay and resulted in a higher ratio of hay to total solid,experiment 3 was conducted to determine how different feed presentations affect the sorting behavior of older dairy calves.Thirty-six(36)female calves(95.5 ± 7.9 kg,78 ± 1.5 d)were fed in same manner from birth to week 11,then they were exposed to 1 of 3 feed presentation treatments including solely concentrate(SOLE),concentrate and hay offered as a mixture(MIX),or as separate components(SEPA)during week 12 to week 15.A novel TMR was subsequently supplied from week 16 to week 28.Calves exposed to MIX sorted in favor of concentrate when mixture was offered,and a carry-over effect was found after transition to TMR.However,calves fed SEPA sorted for long particles(106.9%)in the first two weeks after transition to TMR,whereas calves fed SOLE and MIX sorted against them(84.8%and 88.8%).Calves exposed to SOLE and MIX tended to sort for fine particles(103.2%and 100.8%),whereas calves exposed to SEPA did not(95.5%).At week 28,no treatment effects on feed sorting were found.Overall,early exposure of calves to different solid feed presentations can affect choice of feed in a short-term,but may not have a long lasting effect.Provision of both concentrate and hay as separate components early in life are probably the most effective way to increase consumption of long particles and reduce sorting for smaller grain particles. |
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