Abstract
There is increased interest in precision-feeding systems that account for individual-animal variation and temporal dairy herd dynamics to increase feed-efficiency and reduce environmental footprints. The Ruminant Farm Systems (RuFaS; Hansen et al., 2021) model simulates individual animals on a daily timestep using a stochastic, Monte Carlo framework to represent the phenotypic diversity and population dynamics expected in a dairy herd. Within RuFaS, individual animal nutrient requirements are used to inform pen-level diet formulations and feed delivery. However, nutritional requirements for feeding dairy cattle were recently updated via consideration of both animal and diet-related factors. Our aim was to calculate individual animal predictions for dry matter intake (DMI), as well as energy and metabolizable protein requirements, and compare the methods described in the 7th (NRC, 2001) and 8th (NASEM, 2021) editions of the Nutrient Requirements for Dairy Cattle. For that purpose, we simulated dairy herds (ca. 6,000 individual Holstein animals per simulation, mean adult body weight = 671 kg, standard deviation = 79, mean daily milk production = 39.8 kg·day-1·cow-1 , standard deviation = 7.5) for 10+ year time periods with an updated version of RuFaS. The simulated herds provided a wide range of values with which to test the nutrient requirement models, and their implications. The NASEM DMI estimates were less across the board but began to converge towards NRC calculated values at the larger simulated animal body weights. The principal differences in energy requirements between the two models (NRC vs. NASEM) were: 1) predicted requirements for pregnancy were significantly greater for NASEM than NRC across all life history stages; 2) NASEM displayed slightly greater energy requirements for growth in first and second lactation cows, and; 3) NASEM predicted decreased maintenance requirements for all heifer stages but the opposite was true for mature cows. Metabolizable protein requirements were greater following NASEM calculations in heifers over 300 kg, but strikingly similar to NRC-computed values for lactating cows. Overall, results from this modeling study align with our expectations and demonstrate successful implementation of the two nutrition models within the RuFaS model. These outputs confirm the usefulness of data obtained to explore applications of the two nutrient requirement models under different precision feeding management practices and, to some extent, to quantitatively evaluate their viability of the models in edge cases that can occur within the expected variation of a herd’s population. Future work will explore downstream consequences of the nutrient requirement models within the automated, least-cost ration formulation framework using nonlinear programming and metrics related to manure output and storage. These data will guide further developments of RuFaS as whole farm simulation model and provide insights into expected variation in nutritional requirements within a dynamic set of animals.
Abstract
Our objective is to explore the predicted mitigation potential of 3-nitrooxipropanol (3-NOP) when added to typical diets for lactating cows across the United States (US). Three forage-to-concentrate ratios (F:C on a dry matter basis, DM) were considered: 70:30, 50:50, and 30:70, respectively. Corn silage (CS) was combined with a second forage source (F2) at 70:30, 50:50, and 30:70 for each F:C. The F2 option was either one of 3 grass-legume silage mixtures (GLS), or legume hay (LH). Twenty US regional by-product-based concentrate mixes (BP) were formulated. Inclusion rates of the BP and corn grain were flexible within the concentrate component of the diet to meet the energy (1.52 ± 0.040 Mcal/kg DM of NEL), and crude protein (16.0 ± 0.30% DM of CP) requirements for a cow eating 24 kg of DMI/d and producing 36 kg of milk/d. Chemical composition of feedstuffs was taken from tabulated values. In total, 144 diets were formulated. Methane yield (CH4/DMI; g/kg) for each diet was predicted using an equation by Niu et al. (2018; Eq. 42) including both animal factors (energy corrected milk, milk fat and protein contents, and body weight) and diet factors (ether extract (EE) and neutral detergent fiber (NDF), both as % DM). Across all diets, the CH4 yield estimates ranged from 17.6 to 19.4 g/kg DMI. Mitigation potential of 3-NOP (% of reduction in CH4 yield emission) was assessed at a fixed dosage of 70 mg/kg DM using the recent Kebreab et al. (2023) equation built from the 3-NOP dose (mg/kg of DM), and NDF, EE, and starch contents in the diet (% DM). Within the 144 diets evaluated, CH4 yield emissions can be reduced from 8% to up to 38%. The greatest reduction was achieved from an initial CH4 yield of 18.3 g/kg when 3-NOP is added to a Northeast diet containing 70% of concentrate (42% DM BP mix) and LH as the F2 source at 21% of the total diet (DM basis). For the given diet offered to a herd of 1,000 lactating cows and assuming a Global Warming Potential (GWP) for CH4 of 34, we estimated that the addition of 3-NOP has the potential to decrease enteric CH4 production up to 2,070 t of CO2-eq per year.
Abstract
The improved reproductive performance and the use of sexed semen have resulted in an oversupply of heifer replacements, presenting an opportunity to use beef semen to produce crossbred calves of higher value for the beef market in combination with sexed semen to expedite the genetic progress. To quantify genetic progress and economic benefits of different semen-use strategies, a simulation study was conducted using a version of the Ruminant Farm Systems model modified to represent genetic inheritance through a net merit (NM) trait assigned to all animals. The study considered 2 heifer semen use strategies: sexed semen used on the top 50% of heifers (H1) or all heifers (H2), and 2 cow semen use strategies: sexed semen used on the top 25% of cows, with beef semen used on the bottom 25% of cows (C1), or sexed semen used on the top 50% of cows, with beef semen used on the remaining cows (C2). Five scenarios were evaluated: (1) conventional semen used for all eligible animals (control), (2) H1C1, (3) H1C2, (4) H2C1, and (5) H2C2. We simulated a herd of 1,000 cows that was maintained through a monthly purchase and sale of springers. Male and crossbred calves were sold while female calves were retained for breeding. To assign NM for animals at the start of the simulation we randomly selected values from CDCB NM percentile tables for year 2022 and adjusted the values downward based on the average linear increase in NM over the animals’ lifespan. We defined genetic progress as the simulated change in NM over a 10-year period. The NM increase of top sires and market replacements was assumed to be the same as the average rate during the past 5 years. Compared with the control, the 4 mixed semen strategies increased the NM annual rate of increase for cows and heifers by $24 to $30 and $22 to $26, respectively. Furthermore, the H1C2 strategy covered the extra reproduction cost through the income generated by selling crossbred calves, without including the positive impact of genetic progress on herd performance. These results highlight the value of using sexed semen and beef semen to enhance the genetic progress and economic benefits of the herd.
Abstract
During the dry period, dairy cows eat less and are commonly fed with a decreased energy content in the diet. These factors will impact the expected enteric methane (CH4) emissions when compared to lactating animals. Our objective is to explore the variability in predicted enteric CH4 emissions (g/d) of dry cows fed typical diets in the United States (US) using existing empirical equations. Three forage-to-concentrate ratios (F:C on a dry matter basis, DM) were considered: 80:20, 65:35, and 50:50. Corn silage (CS) was combined with a second forage source (F2) at 50:50, 40:60, and 70:30 for each F:C ratio. Thirty-six by-product-based concentrate recipes were formulated to meet desired diet nutrient composition across four regions in the US: Midwest (MW), Northeast (NE), South (S), and West (W). Inclusion rates of the by-product-based concentrate-mix and corn grain (CG) were flexible within the concentrate component of the diet. A total of 144 diets were formulated to meet the energy (1.39 ± 0.04 Mcal/kg of NEL), and crude protein (15.0 ± 0.30% of CP) requirements for a dry cow (BW = 650 kg) eating 12.5 kg of DMI/d. Chemical composition of feedstuffs was taken from tabulated values. Enteric CH4 emissions were predicted using two equations by Moraes et al. (2014), which were specifically developed for this animal category from indirect calorimetry measurements. The first equation uses gross energy intake (GEI) as a single prediction variable, whereas the second equation incorporates both GEI and dietary ether extract (EE). The last model is included within the most recent edition of the Nutrient Requirements of Dairy Cattle (NASEM, 2021). On average (±SD), CH4 emissions were 253 ± 1.4 and 250 ± 1.2 g/d, for the first and the second equation, respectively. Emissions estimates for the second model ranged from 248 to 253 g/d. The lowest prediction was obtained from a diet with 80F:20C ratio, 56% inclusion of grass-legume silage mixture as F2 source, and W type by-product concentrate fed at 8%. The opposite was found with a combination including 50F:50C ratio, 25% of legume hay, and W type by-product concentrate fed at 38% inclusion in the diet. Our results quantify the extent of expected variation in CH4 emissions from dry cows fed diets that are representative of those used in the US dairy industry.
Abstract
In addition to the level of intake, physical and chemical nature of feed play a key role in CH4 emissions from ruminant livestock. Empirical models combining these factors are considered in recent updates of feed evaluation systems worldwide. Our objective is to explore the variability in predictions of enteric CH4 emissions (g/d) of lactating cows fed contrasting diets in terms of concentrate proportion and including commonly used by-products for ration formulation across the United States (US). Three forage-to-concentrate ratios (F:C on a dry matter basis, DM) were considered: 70F:30C, 50F:50C, and 30F:70C, respectively. Within the forage component of the diet, corn silage (CS) was combined with a second forage source (F2), which is one of three grass-legume silage mixtures, or legume hay (LH), in fixed proportions (DM basis) as follows: 70CS:30F2, 50CS:50F2, and 30CS:70F2, respectively. Twenty by-product-based concentrate recipes were formulated for four US regions, namely: Midwest (MW), Northeast (NE), South (S), and West (W). Inclusion rates of the by-product-based concentrates and corn grain (CG) were flexible within the concentrate component of the diet. A total of 144 diets were formulated to meet the energy (1.52 ± 0.040 Mcal/kg of NEL), and crude protein (16.0 ± 0.30% of CP) requirements for a Holstein cow (BW = 600 kg), eating 24 kg of DMI/d, and producing 36 kg of milk/d. Chemical composition of feedstuffs was taken from tabulated values. Enteric CH4 emissions were predicted using a modified equation by Nielsen et al. (2013), which is included within the most recent edition of the Nutrient Requirements of Dairy Cattle (NASEM, 2021), or an equation proposed by Niu et al (2018), which better performed for US conditions in their dataset. For both equations, DMI is the main animal-related predictor. Dietary concentrations of fatty acids (FA) and digested neutral detergent fiber (dNDF) are incorporated within the first equation, while NDF content is included in the second equation. On average (±SD), CH4 emissions differed depending on the empirical equation used: 447 ± 9.8 vs 421 ± 7.6 g/d, for Nielsen et al., 2013, Niu et al., 2018, respectively. Emissions estimates from the Niu et al (2018) model ranged from 403 to 440 g/d. The lowest value was obtained from a diet with 30F:70C ratio, 21% inclusion of LH as F2 source, and W type by-product concentrate fed at 42%. The opposite was found with a combination including 70F:30C ratio, 49% of grass legume silage mixture (predominantly grass), and S type by-product concentrate fed at 25% inclusion in the diet. Dairy cattle diets in the US vary widely and results from this modeling study describe the extent to which existing empirical equations to predict CH4 emissions can reflect this variability.