title: Short-term response in milk production, dry matter intake, and grazing behavior of dairy cows to changes in postgrazing sward height.
abstract: Postgrazing sward height (PGSH) can be altered to adjust the allowance of grass in the dairy cow's diet. This study aimed to investigate the short-term dairy cow response to a change in postgrazing height in early lactation. Ninety Holstein Friesian spring-calving cows were randomly assigned across 3 postgrazing height treatments (n=30): 2.7 cm (severe), 3.5 cm (low), and 4.2 cm (moderate) from February 14 to April 24, 2011. From April 25, animals were rerandomized within each treatment to graze across 2 postgrazing heights: 3.5 cm (low) or 4.5 cm (high). Animal production measurements were taken from April 4 to 24 (measurement period 1; M1) and from April 25 to May 15 (measurement period 2; M2). The 6 treatments (n=15) of M2 were severe-low, severe-high, low-low, low-high, moderate-low, and moderate-high. During M1, increasing postgrazing height from severe to low to moderate linearly increased daily milk yield (21.5, 24.6 and 25.8 kg/cow per day) and grass dry matter intake (GDMI; 13.2, 14.9, and 15.8 kg of DM/cow per day). Milk solids yield was reduced in the severe (-1,518 g/cow per day) treatment when compared with the low and moderate cows (1,866 g/cow per day, on average). The milk yield (MY) response to change in PGSH between M1 and M2 (VM1-M2) was established using VM1-M2 MY=-1.27-1.89 × PGSHM1 + 1.51 × PGSHM2 (R(2)=0.64). The MY response associated with each treatment between M1 and M2 (3 wk) were -1.03 kg/cow for severe-low, 0.68 kg/cow for severe-high, -2.56 kg/cow for low-low, -1.11 kg/cow for low-high, -4.17 kg/cow for moderate-low, and -2.39 kg/cow for moderate-high. The large increase in energy intake in severe-high between M1 and M2 was achieved through higher GDMI per minute and GDMI per bite, which supported the positive change in MY. Treatments low-high, moderate-low, and moderate-high recorded the highest overall cumulative milk yield (74 kg of milk solids/cow) over the 6-wk period, whereas severe-low and severe-high had the lowest (65 kg of MS/cow). From the animal responses observed in the present study, imposing a postgrazing height of 3.5 cm in early spring provides the opportunity to increase postgrazing height thereafter; the cow increases GDMI accordingly and converts the additional energy intake into milk output. The equations established in this paper provide a decision tool for dairy farmers to anticipate the animal response when postgrazing height is altered or maintained around the tenth week of lactation.
authors.affiliation: Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland; School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, Ireland. Electronic address: elodie.ganche2@gmail.com.
authors.forename: E
authors.initials: E
authors.lastname: Ganche
authors.affiliation: Institut National de Recherche Agronomique, 35590 St. Gilles, France.
authors.forename: L
authors.initials: L
authors.lastname: Delaby
authors.affiliation: Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.
authors.forename: M
authors.initials: M
authors.lastname: O'Donovan
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin, Ireland.
authors.forename: T M
authors.initials: TM
authors.lastname: Boland
authors.affiliation: Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.
authors.forename: E
authors.initials: E
authors.lastname: Kennedy
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003612:Dairying; D004032:Diet / Q000662:veterinary*; D002149:Energy Intake; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D007774:Lactation / Q000502:physiology*; D008892:Milk; D006109:Poaceae; D012621:Seasons
keywords: dairy cow; grazing; milk response; postgrazing height