Evaluation of corn silage quality and its effects on dairy cow performance
Open Access
- Author:
- Cueva Welchez, Sergio
- Graduate Program:
- Animal Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 06, 2024
- Committee Members:
- Adele Turzillo, Program Head/Chair
Christopher Canale, Special Member
Alexander Hristov, Chair & Dissertation Advisor
Tara Felix, Major Field Member
Guojie Wang, Outside Unit & Field Member
Kevin Harvatine, Major Field Member - Keywords:
- dairy cow
corn silage
amylase enabled corn silage
rumen fermentable organic matter - Abstract:
- Corn silage (CS) is the main forage source for dairy diets in the United States. Selection of high-quality corn silage is necessary to increase profit and overall resilience of dairy farms. Novel hybrids entering the market must be closely investigated to determine their effects on lactational performance. Furthermore, developing tools to assess CS quality that are also practically applicable by farmers could prove to be extremely beneficial. A series of 3 corn silage experiments were conducted. This series of experiments aimed to investigate the effects of an amylase-enabled corn silage hybrid (ACS) on lactational performance of lactating dairy cows (Experiment 1), investigate the relationship between corn silage's Rumen Fermentable Organic Matter Index (RFOMI) determined by in vitro (IV) and in situ (IS) methods and lactational performance variables of dairy cows (Experiment 2), and evaluate the milk production and gas emission effects of feeding CS with differing rumen fermentable fiber and starch to dairy cows (Experiment 3). In experiment 1, 48 mid-lactation Holstein cows were enrolled in the study and assigned to 1 of 3 dietary treatments in a 10-week randomized complete block design. Treatments were a control diet formulated with a conventional hybrid CS (CON), a diet with ACS replacing CON (ADR; amylase corn silage direct replacement diet), and a modified ADR diet adjusted to match the starch levels of CON (ASR; amylase corn silage starch parity diet). Corn silage was included at a 40% inclusion rate of TMR dry matter (DM) in all diets. An IS study was performed to assess the effects of ensiling phase on nutrient degradability of ACS and conventional CS. Dry matter intake (DMI), milk yield (MY), feed efficiency, enteric methane emissions, and apparent total-tract nutrient digestibilities were recorded and analyzed in this experiment. For experiment 2, 40 fresh CS hybrids were initially assessed using their RFOMI calculated using single-timepoint IV measurements for NDF (NDFD) and starch digestibilities (StD). The RFOMI is intended to represent ruminally digestible corn silage organic matter and was designed to facilitate the corn silage selection process performed by dairy producres. Following the initial screening, 10 hybrids with contrasting RFOMI (i.e., 5 low vs high RFOMI CS hybrids) were selected for analysis of nutrient disappearance using an IS approach. Additionally, a meta-analysis of 17 feeding trials was conducted to explore the relationships between CS RFOMI and lactational performance metrics. The dataset was comprised of studies conducted at William H. Miner institute and The Pennsylvania State University from years 2011 to 2021. For experiment 3, 48 Holstein cows were enrolled in the study. Before the commencement of the trial, post-ensiling nutrient analyses were conducted to assess the compositional changes in CS hybrids throughout the ensiling process, particularly focusing on changes in rumen-fermentable starch (RFST) and rumen-fermentable NDF (RFNDF) concentrations. Sequential differences in CS RFST to RFNDF ratios were observed among hybrids. Cows were blocked and assigned to 1 of 4 dietary treatments in a 10-week randomized complete block design. Treatment diets were TMR containing 50% CS of the dietary DM, formulated for a physical DM replacement with CS hybrids that were similar in RFOMI but had different RFST:RFNDF ratios. The RFST:RFNDF ratios of the CS hybrids fed in this study were of 1.62 (CS1.62), 1.85 (CS1.85), 1.92 (CS1.92), or 2.08 (CS2.08). The MIXED procedure of SAS, version 9.4, was employed for data analysis, allowing for the evaluation of polynomial linear or quadratic effects of RFST:RFNDF ratios on dairy performance variables. In Experiment 1, it was determined that direct replacement of control with ACS resulted in similar ECM yield, despite greater starch concentration of the control silage. The ACS had 3-% units greater in vitro fiber digestibility, which increased daily enteric methane emission and emission intensity. Addition of corn grain to the ACS diet to achieve a starch concentration comparable to that in the control diet had no effect on the lactational performance, methane emissions and ruminal fermentation. It did, however, decrease milk true protein concentration and yield relative to cows fed the conventional CS. It was concluded that replacing control CS with ACS with 19% lower starch concentration had no statistically significant effects on dairy cow performance, except DMI was greater for ADR during the initial stages of the experiment. Results from Experiment 2 suggested that selection of CS hybrids based on 7.7%-unit difference in their RFOMI, calculated using single-timepoint IV measurements for NDFD and starch degradability from a commercial laboratory, aligned well with our IS nutrient disappearance data. Results from the meta-analysis suggest that CS RFOMI is positively related with DMI, MY and ECM yield but not feed efficiency of dairy cows fed diets in which CS represented over 36% of DMI. However, the relatively low coefficients of determination in our analysis indicate that CS RFOMI alone does not explain a large portion of the variation seen in the data. A discrepancy between in vitro and in situ CS StD measurements was observed suggesting that further research may be needed to determine the most accurate methodology for starch degradability analysis of CS hybrids. From experiment 2 we concluded that CS RFOMI can be used as a tool by dairy farmers to select for CS quality and, when matched with adequate diets, can potentially lead to improved animal performance through increase in feed intake and milk yield. In experiment 3, when CS hybrids with similar post-ensiling RFOMI, but differing RFST and RFNDF concentrations were included in the diet at a 50% dietary DM inclusion rate, a quadratic effect on DMI was observed, where CS with the lowest RFST:RFNDF ratio had the greatest DMI, followed by cows fed the CS hybrid with the greatest RFST:RFNDF ratio. Increasing corn silage RFST:RFNDF ratio linearly increased milk yield of dairy cows but did not affect ECM yield. Methane emission yield (g per kg of DMI) and apparent total tract DM and OM responded quadratically in dairy cows fed increasing proportions of RFST to RFNDF concentrations in corn silage. In that experiment, we also noted that changes in the nutrient composition of fresh CS hybrids during the ensiling process affect both the RFST and RFNDF content of the silages. For experiment 3, it was concluded that increasing corn silage RFST to RFNDF concentration tends to induce a linear increase in milk yield, but feed efficiency, ECN feed efficiency, DMI and methane yields exhibited a quadratic response. We also conclude that CS hybrid selection tools based on ruminal digestibility, such as the RFOMI, should be further developed to integrate fresh CS nutrient values with the chemical changes that occur during ensiling.