PSXI-17 Performance of beef cattle overwintered on bale-grazed pasture or in a dry lot in south-central North Dakota

The performance of beef cows managed in two overwintering environments, bale-grazed pasture or dry lot pens, was evaluated in a study conducted over four winters, from 2016 to 2019. Non-lactating pregnant Angus cows (2016, n = 32, body weight [BW] = 599 ± 68 kg; 2017, n = 40, BW = 620 ± 59 kg; 2018, n = 40, BW = 643 ± 47; 2019, n = 40, BW = 624 ± 30) were divided into four groups of similar body weight and randomly assigned to either bale grazing paddocks or dry lot pens. Cows in both housing scenarios were fed the same hay (7.5% CP; 51.7% TDN). Two-day body weights were taken at the start and end of the study. Two independent observers assigned body condition score (BCS) using a 9-point system (1 = emaciated, 9 = obese at the start and end of the study. Keeping cows on pasture or in dry lot pens did not influence (P > 0.05) final BW and BCS. However, daily gains and BCS change were greater (P ≤ 0.05) in bale-grazed cows relative to cows kept in dry lot pens. Birth weights, weaning weights and daily gains of calves from cows kept in the two overwintering environments were similar (P > 0.05). This study suggests that there are no advantages to keeping cows in dry lot pens in winter as long as cows are protected from wind and have adequate access to water and feed. In certain situations, such as in blizzards, it may be an advantage to keep cows on pasture where they can access feed since challenging weather conditions can prevent access to cows in dry lot pens.

PSII-13 Impact of maternal phosphorus intake on colostrum quality, calf growth, and calf immunoglobulin concentrations in primiparous beef cows

The objective of this experiment was to evaluate the effect of maternal phosphorus intake on growth and health of their calves. Treatments were 1) a free-choice mineral containing no supplemental P or 2) a free-choice mineral with 4% supplement phosphorus. Primiparous crossbred Angus beef cows (n = 36) were stratified by body weight and pregnancy status (bred by artificial insemination or natural service) then assigned to pasture groups (4 groups, 2/treatment, 9 heifers/group). These bred heifers had been receiving these same dietary treatments from 30 days after weaning until confirmation of pregnancy. Eighteen bred heifers from each treatment were selected randomly to continue into this experiment. At calving, colostrum and blood samples were collected from a subset of 12 heifers/treatment (6/group) and evaluated. Body weights and calf viability scores were obtained for all cattle. Data were analyzed using the MIXED (for continuous data) and GLIMMIX (for scoring data) procedures of SAS using group as the experimental unit. Cows grazed mixed grass pastures; monthly forage samples ranged from 0.28 to 0.36% P. There were no differences (P > 0.10) for cow body weight during gestation, calf birth weight, calf viability scores at birth, or calf weight at an average age of 21 days. There were also no differences (P > 0.10) in colostrum components (fat, protein, lactose, and IgG), or in the serum IgG or plasma mineral concentrations for both cows and calves 48 hours after parturition. All calves were sampled at approximately 21 days of age and there were no treatment differences (P > 0.10) in serum IgG concentrations. There were no benefits to supplementing gestating heifers with phosphorus when they grazed pasture with a history of fertilization with livestock manure.

Effect of Post-Grazing Sward Height, Sire Genotype and Indoor Finishing Diet on Steer Intake, Growth and Production in Grass-Based Suckler Weanling-to-Beef Systems

This study evaluated the effects of post-grazing sward height (PGSH, 4 or 6 cm) on herbage production, its nutritive value, dry matter (DM) intake, grazing behaviour and growth of early- (EM) and late-maturing (LM) breed suckler steers (n = 72), and the subsequent effect of indoor finishing diet (grass silage + 3.8 kg concentrate DM/head daily (SC), or grass silage only (SO)) on performance and carcass traits. Animals rotationally grazed pasture for 196 days, followed by indoor finishing for 119 days. At pasture, daily live-weight gain (LWG) was 0.10 kg greater for PGSH-6 than PGSH-4, resulting in a tendency for carcass weight to be 11 kg heavier. Although EM had a 0.10 kg greater daily LWG at pasture than LM, carcass weight did not differ between the genotypes. There was a genotype × PGSH interaction for carcass fat score, whereby there was no difference between EM-4 (8.83, 15-point scale) and EM-6 (8.17), but LM-6 (7.28) was greater than LM-4 (6.33). Although concentrate supplementation during indoor finishing increased carcass weight (+37 kg) and fat score (1.75 units), the majority of steers (83% of EM and 78% of LM) achieved a commercially-acceptable carcass fat score (6.78) at slaughter in the grass-forage-only system.

Landscape position, sampling time and tillage, but not legume species, affect labile carbon and nitrogen fractions in a four-year-old rejuvenated grazed pasture

Termination by tillage is one strategy used for regenerating pasture stands. Yet, research gaps exist on how tillage affects carbon (C) and nitrogen (N) forms and amounts in western Canadian soils. We measured total soil organic C (SOC), dissolved organic C (DOC), total dissolved N (TDN), light fraction organic C (LFOC) and N (LFON), microbial biomass C (MBC) and N (MBN), and inorganic N as indicators of soil organic matter (SOM) dynamics. After tillage termination in fall 2018, we sampled soils (0‒10cm; 0‒15cm) under three legume species (alfalfa, cicer milkvetch and sainfoin) three times (spring, summer and fall of 2019) across three landscape positions. Legume species did not affect the measured parameters. Over time, tillage affected DOC, TDN, and inorganic N. Averaged across three pasture legumes and three landscape positions, tillage increased DOC 29% by summer. Fall-applied tillage led to 59% and 33% higher TDN in the succeeding summer and fall. Inorganic N increased by 14% and 40% across landscape positions and sampling after tillage. Averaged across landscape positions, MBC decreased by 31% from spring to summer and increased by 51% from summer to fall. However, MBN increased by 53% and decreased by 5% within the same period. The seasonal fluctuations in MBC/MBN reflected variations in moisture, temperature, and substrate quality. Total SOC, LFOC, and LFON increased on the upper slopes and fall sampling time. Although single intensive tillage did not affect total SOC, several tillage operations could accelerate SOM loss and reduced total C storage over time.

Using new insights in grazing management to buffer the impacts of climatic variability on pasture resilience

Pasture is the main source of nutrition for the New Zealand ruminant livestock industry. Changing climatic conditions and relentless intensification are putting the ability of pastures to provide that nutrition under pressure. Recent understanding of the interactions between grazing management and the life cycle of roots, leaves and seedheads of pasture species creates further opportunities to increase pasture resilience. Root production is directly related to, though lagging, leaf production and turnover. Tiller production is modified by temperature and seedhead production. Matching grazing patterns to maximise the production of each of these features is generally impossible at the farm scale. However, matching some of these characteristics on some of the farm can be achievable, and have long-lasting benefits for pasture resilience. Therefore, grazing management practices such as deferred grazing in late spring, summer and autumn may be used both to provide a boost to root and tiller production, and to transfer feed from one grazing period to another. Changing our winter management practices away from intensive daily allocations towards 4-day shifting may also increase early spring production, while reducing summer grazing pressure in droughts will aid pasture productivity and persistence in the long term. These techniques have the potential to ensure that the future nutritional needs of grazing ruminants will continue to be met by grazed pasture.