The effect of concentrate supplement type on milk production, nutrient intake, and total-tract nutrient digestion in mid-lactation, spring-calving dairy cows grazing perennial ryegrass (Lolium perenne L.) pasture

摘要

The objective of this study was to evaluate the effectof concentrate supplement type on milk production,nutrient intake, and total-tract nutrient digestionin lactating dairy cows grazing mid-season perennialryegrass (Lolium perenne L.; PRG) pasture. Twelveprimiparous (mean ± standard deviation; 95 ± 30 din milk and 470 ± 43 kg of body weight) and 68 multiparous(99 ± 24 d in milk and 527 ± 64 kg of bodyweight) lactating dairy cows were blocked based onpre-study milk yield and parity and randomly assignedto 1 of 4 dietary treatments. The 4 dietary treatmentswere a non-supplemented PRG control (PRG); PRGsupplemented with 4.4 kg of dry matter (DM) per cowper day of citrus pulp and 0.067 kg of DM/cow perday of urea (PRG+C); PRG supplemented with 0.8kg of DM/cow per day of heat-treated soybean meal(PRG+PP); and PRG supplemented with 3.1 kg ofDM/cow per day of a combination of heat-treated soybeanmeal and citrus pulp (PRG+C+PP). The studyconsisted of a 2-wk adaptation period and a 10-wkperiod of data collection. Weekly measurements of milkyield, body weight, body condition score, and feedingand rumination time were made. Nutrient intake andtotal-tract digestibility were measured during wk 6 ofthe study. A large soil moisture deficit was experiencedduring the study that probably reduced herbage growthrate and likely altered the chemical composition of thePRG offered when compared with typical mid-seasonPRG. Total dry matter intake was increased in cows fedPRG+C compared with cows fed PRG and PRG+PPand was similar to cows fed PRG+C+PP (18.0, 15.9,16.4, and 17.2 ± 0.41 kg of DM/d, respectively). Theapparent total-tract neutral detergent fiber digestibilityof cows fed the PRG+C diet was lower compared withthe PRG and PRG+PP diets and was similar to thePRG+C+PP diet (0.67, 0.70, 0.70, and 0.69 ± 0.01g/g, respectively). The energy-corrected milk (ECM)yield of cows fed PRG+C+PP was highest (23.7 kg/d),PRG+C was intermediate (22.2 kg/d), and PRG waslowest (20.8 kg/d). Cows fed PRG+PP produced moreECM (22.9 kg/d) compared with cows fed PRG andproduced similar ECM compared with cows fed PRG+Cand PRG+C+PP diets. The PRG+PP diet increasedmilk protein yield compared with the PRG diet,tended to increase milk protein yield compared withthe PRG+C diet, and was similar to the PRG+C+PPdiet. Milk fat concentration and the composition ofmilk fat were not influenced by treatment. The resultsdemonstrated that, for cows consuming pasture-baseddiets, increasing metabolizable protein supply allowedhigher milk yield as metabolizable protein was morelimiting than metabolizable energy. However, due tothe large soil moisture deficit experienced during thisexperiment, caution is recommended when extrapolatingthese results to cows consuming typical mid-seasonPRG herbage.