The development of systems to improve the utilisation of grass and forage in beef production systems

Abstract

A series of studies were undertaken which were aimed at developing systems to increase the utilisation of grass and forage in beef production systems. Specifically, this thesis addresses four key knowledge gaps which were identified following a comprehensive review of the scientific literature. The objectives were to:
1. To identify the effects that new and old swards have on nitrogen use efficiency (NUE) under increasing nitrogen fertiliser levels and using weather to predict NUE (Chapter 3)
2. To identify macro and micronutrient content of grass and establish relationships between other macro and micronutrient and quality parameters in fresh herbage (Chapter 4)
3. To identify the effects of sward age and clover content on both sward and animal performance (Chapter 5)
4. Investigation of pre and post weaning treatment on the behaviour and performance of suckler calves and the effect of deferred winter grazing on animal performance (Chapter 6)

Chapter 3 investigates effects of sunshine hours, rainfall, air temperature and nitrogen application rate on the nitrogen use efficiencies of old and new swards. It also aimed to develop prediction equations to calculate NUE using known quantities of N applied and sunshine hours, rainfall, and air temperature. The experiment was conducted over two years (2018 and 2019) over two sites in year 1 and over four sites in year 2. There were four nitrogen rates applied per site which were 0 kg N/ha/yr, 90 kg N/ha/yr, 180 kg N/ha/yr and 270 kg N/ha/yr and herbage was collected on a 21-day cycle. Increasing nitrogen application increased sward herbage production in both old and new swards. The new swards grew more than the old swards by 0.8t/ha. In year 1, August had the greatest herbage growth rates, while in year 2, this was seen in May. This is due to the drought that took place over the summer in year 1, which stunted herbage growth in over the summer months in year 1 and when it began to rain at the end of July the herbage had a sudden surge in growth. The new swards had greater growth rates in May, June, and July than the old swards in year 2. In both years, increasing the N application rate increased the CP levels in the herbage. Although the applied N rates were fixed, together with the with soil N there was a range of 174 – 416 kg N/ha equivalent of total N applied. The NUE’s were very similar and fell between 70 - 98%. Though care needs to be taken for those NUE’s >90% as this is indictive of soil mining, which could be suggesting that the two old swards and one new sward in year 2 at 180 Kg N/ha/yr are mining the soil for N which could be unsustainable in the long term. The best of the equations produced had an R2 = 0.36, this considered N application rate, sunshine hours, rainfall, and air temperature and while the prediction equations are significant, they may be of limited use for predictions due to the low R2. This can maybe be improved with additional weather data added in, such as soil temperature, humidity or air flows.

Chapter 4 investigates the effects that mineral content has on herbage quality and how these minerals interact. This study also aimed to develop prediction equations to calculate sward quality and plant mineral content. The experiment was conducted over two years (2018 and 2019) over two sites in year 1 and over four sites in year 2. There were four nitrogen rates applied per site which were 0 kg N/ha/yr, 90 kg N/ha/yr, 180 kg N/ha/yr and 270 kg N/ha/yr and herbage was cut every 21 days for quality and yield data. The herbage for mineral analysis was collected monthly. Across the season in year 1 every mineral tested for was highly significant while in year 2 all the minerals except for Se and Mn were seen to be significant (P < 0.05) over the growing season. There were four minerals that were affected by increasing the amount of nitrogen with N application level having a positive effect on the amount of Mg and Zn in the fresh grass and a negative effect on Cl- and Mo. In both years Cu was seen have a positive trend with increasing N rate, while Se was seen to have a negative trend with increasing N rate in year 1 only. In year 2, three minerals extra were seen to be not significant in year 1, Na, P and K. There were four sward mineral interactions seen in which Co and Pb were seen to be in greater amounts in the NS than the OS (46% increase and 58% increase between the OS and NS respectively for Co and Pb), while Mg and Mo were seen in lesser amounts in the new swards compared to the old swards (10% decrease and 17% decrease between NS and OS respectively for Mg and Mo). Across the season the herbage for many minerals was above what was needed by the animals, there were four minerals that were seen to be below what was required by the animal for optimal growth, Mg, Na, Zn and Cu at some point over the two years. While there were many interactions seen there were six mineral interactions and one mineral quality interaction seen with a R2 over 0.5, Co/Pb (0.88), Al/Fe (0.75), Co/I (0.63), Al/Co (0.56), I/Pb (0.50), Mg/Zn (0.50) and WSC/Mg (0.54).

Chapter 5 investigates herbage production and quality and animal performance achieved from a recently reseeded sward versus a permanent grassland sward, with or without the inclusion of white clover. The study involved a 2 (Sward age) x 2 (Clover inclusion) factorial design study and was conducted over two years (2019 and 2020). The sward age treatments included permanent grassland (PG) (established 1992) and recently reseeded grassland (RG) (established 2018), and the clover treatments were with clover (C) and without clover. Sward herbage mass was measured weekly using a rising platemeter, botanical separations were also conducted after each grazing rotation, sward quality was measured using near infra-red spectrometry (NIRS) for dry matter (DM), crude protein (CP), acid detergent fibre (ADF), water soluble concentrates (WSC) and metabolisable energy (ME). The swards were grazed with forty-four (Year 1) and forty (Year 2) Stabiliser or Charolais cross Stabiliser steers (12-18 months old). The animals were weighed every two weeks to calculate their average daily gain (DLWG). Sward variables was subjected to REML variance components analysis, and animal variables were subjected to variance analysis. Year influenced herbage production (P0.05) on herbage production, growth rate, pre and post grazing sward heights. Herbage from the RG had a 3.1% higher ADF (P < 0.01) and a 1.5% lower ME (P0.05) effect of either sward age or clover inclusion on animal DLWG. Both grassland reseeding and clover inclusion had no effect on herbage production or animal performance in the current study, though the RG swards had a higher perennial ryegrass populations compared to the permanent pasture swards.

Chapter 6 investigates the effects of two stage weaning and post weaning environment on cattle growth performance and behaviour. Forty-eight spring born Stabiliser and Charolais X Stabiliser steer (n=24) and heifer (n=24) calves were used in a 2 x 2 factorial design. These calves were assigned to one of four treatments: 1) abrupt weaning indoors (AWI), 2) abrupt weaning outdoors (AWO), 3) nose flaps indoors (NFI) or 4) nose flaps outdoors (NFO). The calves were subjected to two methods to record behaviour 1) visual behaviour assessment 2) IceQube pedometers which were attached to the right hind leg, which recorded standing durations, lying duration, and lying bouts at 15-minute intervals. On day 4 calves the nose flaps were inserted in those calves that were subjected to two stages weaning. On day 11 nose flaps were removed, calves were weighed, and calves were either housed in slatted pens or in grass paddocks. Pre weaning the weaning weight did not differ between weaning methods (P > 0.05) and did not differ in weaning behaviours recorded (P > 0.05). There was no effect of either weaning method or environment post weaning on overall calf liveweight (P > 0.05). Those calves that were abrupt weaned (AW) had a greater standing time compared to those using to nose flaps (NF) (P < 0.001) and therefore a shorter lying time during time post weaning for days.

Deferred/extended grazing was capable of maintaining DLWG comparable to those on an average grass silage. The use of nose flaps had no short-term effect on liveweight and had a positive effect of behaviour post weaning and there was no long-term effect of housing environment on calf performance. The use of nose flaps and housing outdoors are a suitable alternative to abrupt weaning and indoor housing post weaning.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Department of Agriculture, Environment and Rural Affairs
Supervisor	Francis Lively (Supervisor) & Nigel Scollan (Supervisor)