This experiment compared Holstein-Friesian (HF) cows of New Zealand (NZ) origin representative of genetics present in the 1970s (NZ70; n = 45) and 1990s (NZ90; n = 60), and a group of HF cows of North American origin with 1990s genetics (NA90; n = 60), which were managed in grazing systems with a range of feeding allowances (4.5 to 7.0 t/cow per yr) over 3 yr. The NZ70 cows had the lowest Breeding Worth genetic index and the lowest breeding values for yields of fat, protein, and milk volume; the NZ90 and NA90 cows were selected to have similar breeding values for milk traits and were representative of cows of high genetic merit in the 1990s. The NZ90 cows had a higher milk protein concentration (3.71%) than either the NA90 (3.43%) or the NZ70 cows (3.41%), and a higher milk fat concentration (4.86%) than the NA90 cows (4.26%) with a level similar to the NZ70 cows (4.65%). The NZ90 cows produced significantly greater yields of fat, protein, and lactose than the NA90 and NZ70 cows. The NZ70 cows had the lowest mean annual body weight (473 kg) but the highest body condition score (BCS; 5.06). Days in milk were the same for the 2 NZ strains (286 d in milk), both of which were greater than the NA90 cows (252 d in milk). There was no genotype x environment interaction for combined milk fat and protein yield (milksolids), with NZ90 producing 52 kg/cow more than the NA90 at all feeding levels. The NZ70 strain had the highest seasonal average BCS (5.06), followed by the NZ90 (4.51) and the NA90 (4.13) strains on a 1 to 10 scale. Body condition score increased with higher feeding levels in the 2 NZ strains, but not in the NA strain. The first-parity cows commenced luteal activity 11 d later than older cows (parities 2 and 3), and the NA90 cows commenced luteal activity 4 and 10 d earlier than the NZ70 and NZ90 cows. Earlier estrus activity did not result in a higher in-calf rate. The NZ70 and NZ90 cows had similar in-calf rates (pregnancy diagnosed to 6 wk; 69%), which were higher than those achieved by NA90 cows (54%). Results showed that the NA90 strain used in this experiment was not suitable for traditional NZ grazing systems. Grazing systems need to be modified if the NA90 strain is to be successfully farmed in NZ. The data reported here show that the NA90 cows require large amounts of feed, but this will not prevent them from having a lower BCS than the NZ strains. Combined with poor reproductive performance, this means that NA90 cows are less productive than NZ HF in pasture-based seasonal calving systems with low levels of supplementation.

No abstract

A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m -3in winter, with the bulk comprising nitrate nitrogen (NO -3 -N). During summer NO -3 -N was near zero and TN mostly comprised organic nitrogen. Maximum concentrations of total phosphorus (TP) and dissolved reactive phosphorus (DRP) were 1.64 and 0.555 g m -3 , respectively, and peaks coincided with spring and autumn applications of phosphorus fertiliser. Ammoniacal nitrogen concentrations exceeded 1 g m -3 on several occasions and mean concentrations at the three sites were 0.165-0.272 g m -3 . Faecal coliform and enterococci bacteria concentrations were 64-26000 and 7-23000 cfuper 100 Received 23 March 1999; accepted 23 June 1999 ml, respectively. Specific yields of TN and NO -3 -N (35.3 and 30.7 kg ha yr -1 , respectively) were much greater than any previously reported for New Zealand pasture catchments, whereas TP and DRP yields (1.16 and 0.54 kg ha yr -1 , respectively) were more in accord with other studies. Greater use of land treatment of liquid wastes will reduce stream inputs of faecal organisms, NH 4 -N and P. M99015

Grazed pastures based on ryegrass species provide most of the feed for dairy cattle in New Zealand. There are many cultivars of perennial (Lolium perenne), annual and Italian (L. multiflorum), and hybrid (L. boucheanum) ryegrasses available for dairy farmers to use in pasture renewal. This study describes an index which ranks ryegrass cultivars relative to a genetic base according to the estimated economic value (EV) of seasonal dry matter (DM) traits. A farm system model was used to derive EVs ($ ha−1 calculated as change in operating profit divided by unit change of the trait) for additional DM produced in different seasons of the year in four regions. The EV of early spring DM was consistently high across all regions, whereas EV for late spring DM was moderate to low. Genotype × environment analysis revealed significant reranking of DM yield among ryegrass cultivars across regions. Hence, separate performance values (PVs) were calculated for two mega‐environments and then combined with the corresponding season and region EV to calculate the overall EV for twenty‐three perennial ryegrass and fifteen short‐term ryegrass cultivars. The difference in operating profit between the highest ranked and lowest ranked perennial ryegrass cultivar ranged from $556 ha−1 to $863 ha−1 year−1 depending on region. For short‐term ryegrasses used for winter feed, the corresponding range was $394 to $478 ha−1 year−1. Using PV for DM yield, it was estimated that plant improvement in perennial ryegrass has added $12–$18 ha−1 year−1 (depending on region) operating profit on dairy farms since the mid‐1960s.

The dairy industry in New Zealand is a significant contributor (7% of GDP) to the national economy. Major current issues for the industry are the lack of cheap, highly-nutritive value feed for cows of high genetic merit for milk yield; the poorer reproductive capacity of these high merit Holstein-Friesian cows; the quantity and skill of farm labour; and the environmental consequences of intensive dairy farming. The industry has responded to these challenges in the following ways. Increased nitrogen fertiliser use has given increased pasture yields, but also increased nitrate leaching and nitrous oxide emission from farms, which in turn has led to research on wintering pads, diet modification and nitrification inhibitors to reduce N losses to the environment. Increased use of supplementary feeds has given improved milk yield per cow, but also increased total farm variable costs, labour requirements and nutrient losses, which A07006;