Beef cow -calf production from fertilized and unfertilized alfalfa-meadow bromegrass and meadow bromegrass -only pasture

A four year (1995--1998) gazing experiment was conducted to determine the effect of pasture species (meadow bromegrass (Bromus biebersteinii Roem & Schult.)---only pastures and alfalfa (Medicago sativa L.)---meadow bromegrass mixed pastures) and fertilization on forage yield and quality and on cow-calf productivity. Four cow-calf pairs were assigned to four pasture treatments (T): alfalfa-grass fertilized (AF), alfalfa-grass unfertilized (AU), grass-only fertilized (GF) and grass-only unfertilized (GU). Each 3.7 ha pasture was sub-divided into five equally sized paddocks and rotationally stocked. Half of the cows in each pasture received a RumensinRTM controlled release capsule (CRC). Suckling calf forage dry matter intake (FDMI) was estimated by determining the difference between net energy required for maintenance and gain, and energy provided by milk. Four year average forage production of AF, AU, GF and GU were 4.9, 4.1, 4.9 and 2.6 +/- 0.24 t DM ha-1 and the average carrying capacities were 200.4, 163.9, 208.7 and 127.6 +/- 3.3 cow grazing days (CGD) ha-1, respectively. The percentage of alfalfa declined (P < 0.05) in the mixed pastures, from 75.4% and 84.1% in 1995 to 32.5 and 40.3% in 1998 for AF and AU pastures, respectively. Consumed forage quality declined as the grazing season progressed. Cow average daily gain (ADG, g d-1) was affected by a pasture treatment by monensin interaction (P < 0.05), monensin use resulted in a higher cow ADG on GU and AU pastures and had no effect when cows gazed GF or AF pastures. Pasture treatment did not affect milk yield or milk composition. Despite differences in nutrient profiles of the animal's diet, cow-calf productivity for AU, AF and GF were similar. The high dietary fibre content of cows grazing the GU pastures reduced calf ADG (P < 0.05). Calves pastured on the GU treatment had the greatest FDMI (5.3 +/- 0.3 kg d-1) followed by the GF pastures (4.1 +/- 0.3 kg d-1); calves on the AF and AU pastures had similar FDMI (3.5 +/- 0.3 kg d -1). Calves had the ability to select a diet that did not greatly compromise their ADG, even when forage quality was limiting. The AU pastures provided the most consistent results under a variety of environmental conditions. Fertilization improved DM yield of grass pastures by 39% and calf gain ha -1 by 37%, therefore, fertilization should be encouraged when precipitation is not limiting.