Restricting dairy cow access time to pasture in autumn: The effects on milk production, grazing behaviour and DM intake of late lactation dairy cows.

Extending the grazing season in pasture based systems of dairy production can increase farm profitability; poor weather and soil conditions can reduce the number of grazing days. The study objectives were to (i) examine the effect of restricted access to pasture in the autumn on the milk production, grazing behaviour and DM intake (DMI) of late lactation spring-calving dairy cows and (ii) establish the effect of alternating restricted and continuous access to pasture on dairy cow production, DMI and grazing behaviour. Cows were randomly assigned to one of four grazing treatments: (i) 22 h (full-time) access to pasture (22H; control); (ii) Two 5-h periods of access to pasture (2×5H); (iii) Two 3-h periods of access to pasture (2×3H); and (iv) alternating between full-time and 3-h access to pasture with no more than three continuous days on any one regime, e.g. Monday - full-time access, Tuesday - 2x3H access, Wednesday - 2x3H access; Thursday - full-time access, etc. (2×3HV). Restricted access to pasture was offered after a.m. and p.m. milking. Swards of similar quality and pregrazing herbage mass were offered. Treatment had no effect on milk yield (13.2 kg/day), milk fat (48.2 g/kg), protein (39.0 g/kg) or lactose content (42.6 g/kg) and milk solid yield (1.15 kg/day). Similarly, there was no effect of treatment on final BW (483 kg) or final BCS (2.66). There was no significant difference in DMI (15.1 kg DM/cow/day) between treatments. There was an effect on daily grazing time, 22H cows (565 min/cow/day) grazed for longest time, however, when the 2x3HV treatment had full-time access to pasture, they had a similar grazing time (543 min/cow/day) to the 22H cows and were similar to the 2x3H treatment on days with restricted access to pasture (357 min/cow/day). The 22H and 2x5H animals had similar grass DMI/min (29.2 g/min), the 2x3HV were higher (33.9 g/min) but were similar to the comparable treatment when offered 2x3H access time (41.6 g/min) and when offered 22H access time (27.7 g/min). The results from this study show how when offered a grass only diet of autumn pasture grazing behaviour can be modified by restricting pasture access time without reducing dairy cow production in late lactation at low production levels. There was also no effect of alternating access time between 22H and 2x3H on milk production and DMI in the 2x3HV treatment. Restricted access time to pasture in autumn may be a strategy which farmers can use to extend the grazing season.

The effect of cultivated mixed-species green fodder on intake, milk production and milk composition of housed dairy goats.

The majority of New Zealand dairy goat farmers utilise cultivated green-fed fodder dominated by perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), but evidence from other ruminant species suggests that milk production may be improved when using a more diverse array of species within the green fodder. The aim of this experiment was to determine whether feeding lactating dairy goats a mixed-species green fodder (MF, consisting of perennial ryegrass, timothy (Phleum pratense L.), prairie grass (Bromus willdenowii Kunth), white clover, red clover (Trifolium pratense L.), lucerne (Medicago sativa L.), chicory (Cichorium intybus L.) and plantain (Plantago lanceolata L.) improves dietary intake, milk yield and composition compared with a standard ryegrass and white clover green fodder (SF). Thirty-six mid-lactation goats were housed indoors in pairs and split into two groups (A and B). The trial was split into three periods - firstly a uniformity period of 6 days, in which all goats were fed a combination of both green fodder types, followed by two treatment periods (P1 and P2) of 12 days, respectively. For P1, group A was fed MF and group B was fed SF, and then the group diets were switched for P2. Goats fed MF had 13% greater dry matter intake and 7% greater milk yield than goats fed SF. In addition, the milk protein and fat concentration of goats fed MF were 4% greater than for those fed SF, whereas there was no effect on milk lactose concentration. There was no treatment effect on the levels of protein, glucose, urea or non-esterified fatty acids in the blood of the goats. An effect of green fodder type on milk fat profile was demonstrated, with proportions of pentadecylic acid (C15:0), cis-vaccenic acid (C18:1 c11), linoleic acid (C18:2 n6) and α-linolenic acid (C18:3 n3) being increased in response to MF consumption. In contrast, iso-C15 and iso-C17 proportions were lesser. In summary, this study demonstrated that goats fed MF increased green fodder intake and milk production compared with goats fed SF. The green fodder type affected the fatty acid profile of goat's milk, with MF increasing the levels of beneficial polyunsaturated omega fatty acids (linoleic and α-linolenic acids).

Using post-grazing sward height to impose dietary restrictions of varying duration in early lactation: its effects on spring-calving dairy cow production.

The objective of this study was to investigate the immediate and carryover effects of imposing two post-grazing sward heights (PGSH) for varying duration during early lactation on sward characteristics and dairy cow production. The experiment was a randomised block design with a 2×2 factorial arrangement of treatments. A total of 80 spring-calving (mean calving date - 6 February) dairy cows were randomly assigned, pre-calving, to one of the two (n=40) PGSH treatments - S (2.7 cm) and M (3.5 cm) - from 13 February to 18 March, 2012 (P1). For the subsequent 5-week period (P2: 19 March to 22 April, 2012), half the animals from each P1 treatment remained on their treatment, whereas the other half of the animals switched to the opposing treatment. Following P2, all cows were managed similarly for the remainder of the lactation (P3: 23 April to 4 November, 2012) to measure the carryover effect. Milk production, BW and body condition score were measured weekly, and grass dry matter intake (GDMI) was measured on four occasions - approximately weeks 5, 10, 15 and 20 of lactation. Sward utilisation (above 2.7 cm; P1 and P2) was significantly improved by reducing the PGSH from 3.5 (0.83) to 2.7 cm (0.96). There was no effect of PGSH on cumulative annual grass dry matter (DM) production (15.3 t DM/ha). Grazing to 2.7 cm reduced GDMI by 1.7 and 0.8 kg DM/cow in P1 and P2, respectively, when compared with 3.5 cm (13.3 and 14.0 kg/cow per day, respectively). Cows grazing to 2.7 cm for both P1 and P2 (SS) tended to have reduced cumulative 10-week milk yield (-105 kg) and milk solids yield (-9 kg) when compared with cows grazing to 3.5 cm for both periods (MM; 1608 and 128 kg/cow, respectively). Treatments that alternated PGSH at the end of P1, SM and MS had intermediate results. There was no interaction between P1 and P2 treatments. There was also no carryover effect of early lactation grazing regime on milk and milk solids production in P3, given the reduction in early lactation milk yield. The results indicate that the diet of dairy cows should not be restricted by imposing a severe PGSH for all of the first 10 weeks of lactation, cows should graze to 3.5 cm for at least 5 of these weeks.

Short-term response in milk production, dry matter intake, and grazing behavior of dairy cows to changes in postgrazing sward height.

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.

Direct and carryover effect of post-grazing sward height on total lactation dairy cow performance.

Grazing pastures to low post-grazing sward heights (PGSH) is a strategy to maximise the quantity of grazed grass in the diet of dairy cows within temperate grass-based systems. Within Irish spring-calving systems, it was hypothesised that grazing swards to very low PGSH would increase herbage availability during early lactation but would reduce dairy cow performance, the effect of which would persist in subsequent lactation performance when compared with cows grazing to a higher PGSH. Seventy-two Holstein-Friesian dairy cows (mean calving date, 12 February) were randomly assigned post-calving across two PGSH treatments (n = 36): 2.7 cm (severe; S1) and 3.5 cm (moderate; M1), which were applied from 10 February to 18 April (period 1; P1). This was followed by a carryover period (period 2; P2) during which cows were randomly reassigned within their P1 treatment across two further PGSH (n = 18): 3.5 cm (severe, SS and MS) and 4.5 cm (moderate, SM and MM) until 30 October. Decreasing PGSH from 3.5 to 2.7 cm significantly decreased milk (-2.3 kg/cow per day), protein (-95 g/day), fat (-143 g/day) and lactose (-109 g/day) yields, milk protein (-1.2 g/kg) and fat (-2.2 g/kg) concentrations and grass dry matter intake (GDMI; -1.7 kg dry matter/cow per day). The severe PGSH was associated with a lower bodyweight (BW) at the end of P1. There was no carryover effect of P1 PGSH on subsequent milk or milk solids yields in P2, but PGSH had a significant carryover effect on milk fat and lactose concentrations. Animals severely restricted at pasture in early spring had a higher BW and slightly higher body condition score in later lactation when compared with M1 animals. During P2, increasing PGSH from 3.5 to 4.5 cm increased milk and milk solids yield as a result of greater GDMI and resulted in higher mean BW and end BW. This study indicates that following a 10-week period of feed restriction, subsequent dairy cow cumulative milk production is unaffected. However, the substantial loss in milk solid yield that occurred during the period of restriction is not recovered.