The effect of molasses nitrate lick blocks on supplement intake, bodyweight, condition score, blood methaemoglobin concentration and herd scale methane emissions in Bos indicus cows grazing poor quality forage
M. J. Callaghan
A G , N. W. Tomkins B C , G. Hepworth D and A. J. Parker E F
+ Author Affiliations
- Author Affiliations
A Ridley AgriProducts Pty Ltd, Toowong, Brisbane, Qld 4066, Australia.
B CSIRO, Australian Tropical Science and Innovation Precinct, JCU, Townsville, Qld 4811, Australia.
C Meat and Livestock Australia, Fortitude Valley, Brisbane, Qld 4006, Australia.
D Statistical Consulting Centre, The University of Melbourne, Melbourne, Vic. 3010, Australia.
E Department of Animal Sciences, The Ohio State University, Wooster, Ohio 44691, USA.
F Department of Veterinary Science, James Cook University, Townsville, Qld 4811, Australia.
G Corresponding author. Email: matthew.callaghan@ridley.com.au
Animal Production Science 61(5) 445-458 https://doi.org/10.1071/AN20389
Submitted: 24 July 2020 Accepted: 29 October 2020 Published: 23 November 2020
Abstract
Context: The Australian government has approved a greenhouse gas (GHG) offset method that requires cattle to consume nitrate in the form of a lick block. Field studies demonstrating the effectiveness of this methodology have not been previously reported.
Aims: This experiment was conducted to determine the effects on productivity and health when nitrate lick blocks were provided as a supplement to grazing beef cattle. We hypothesised that beef cattle given access to nitrate lick blocks would have similar productivity compared with cattle offered urea lick blocks.
Methods: Bos indicus breeding cows (n = 76) grazed a 467-ha paddock near Charters Towers, Queensland, between May and November 2014. A two-way remote automatic drafting system enabled allocation of cattle to different treatments while grazing in a common paddock. Treatments were 30% urea lick blocks (30U), or molasses nitrate lick blocks (MNB). At monthly intervals liveweight (LW), body condition score (BCS), and blood methaemoglobin concentration were recorded. Estimates of individual supplement intake were made on three separate occasions using a lithium marker technique.
Results: Mean daily supplement intake (±s.e.m.) of 30U (122 ± 13 g) was greater (P < 0.001) than MNB (67 ± 8 g). Lesser MNB intake was associated with greater variability for individual supplement intake, a greater proportion of non-consumers of supplement during July (P < 0.05) and reduced voluntary supplement intake until October (P < 0.001). Increasing MNB consumption during October and November was accompanied by elevated blood methaemoglobin concentration (P < 0.001). It was estimated that cattle offered MNB had insufficient supplementary nitrogen intake throughout the study to resolve rumen degradable nitrogen deficiency from grazed forage. Consequently, cattle provided access to MNB demonstrated conceptus free liveweight loss and lesser BCS compared with cattle treated with 30U (P < 0.001).
Conclusion: Nitrate lick blocks were ineffective as a dual-purpose non-protein nitrogen supplement and methane mitigant for beef cattle grazing poor quality forage. Further field experiments are required to determine if there may be situations where this GHG offset methodology is efficacious.
Implications: Caution is advised in implementing GHG mitigation methods that involve the use of nitrate lick blocks.
Keywords: Australian Carbon Credit Units, carbon economy, cardio-vascular challenge, cattle, Emissions Reduction Fund, greenhouse gas, greenhouse gas offset, lick blocks, methane, methaemoglobinaemia, nitrate, urea, protein supplement, supplementation.
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