Nitrate poisoning in cattle

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

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.

Water Quality for Grazing Livestock I

Water is the most important nutrient for rangeland livestock. However, competition with municipalities, industry, and other water users often results in grazing livestock being forced to use water supplies that are less than perfect. Surface water in western rangleands are often contaminated by mineral extraction, irrigation runoff and other human activities. Mineral contaminants in drinking water are additive with similar contaminants in feedstuffs. The goal of this and the subsequent article is to provide producers and veterinarians with the basic background to make informed decisions about whether a given water supply is "safe" for livestock.

On the pathogenesis of abortion in acute nitrite toxicosis of pregnant dairy cows

Six cows, 220 to 260 d pregnant, were used to study possible abortifacient effects of absorbed nitrite. Maternal and fetal bloodvessels were catheterized. Nitrite was infused intravenously (i.v.) for 30 minutes on Days 1, 3 and 5, commencing at least 5 d postcatheteration. The dose used was 7, 9.5 and 12 mg NO(2)(-)/kg bodyweight, respectively. Nitrite caused a dose-related (P < 0.05) conversion of maternal hemoglobin (Hb) into methemoglobin (MHb); a 30 to 50% decrease of mean arterial bloodpressure; an increase in heart rate, with dose-related recovery periods; and a decrease in partial oxygen tension (PO(2)) of maternal blood. Maternal partial carbon dioxide tension (PCO(2)), pH and electromyographic activity of the uterus were unchanged. Fetal changes included a small increase in MHb content, variable changes in heart rate (tachycardia and bradycardia), and decreases in fetal PO(2), with considerable differences between animals. All calves were born alive. Three cows calved early, 2 to 3 d after the highest nitrite dose. The hematological and cardiovascular data suggest that these three fetuses experienced a more serious hypoxemic stress than the other fetuses.

Toxicologic problems in food animals affecting reproduction

Because a significant number of toxins affect food animal reproduction, the investigating clinician should be aware of their presence and action. If the clinician is confronted with infertility and abortions, the biotoxins, plant estrogens, nitrates, fescue, and selenium-accumulating plants should be considered. The region of the country will limit the considerations. Outbreaks of congenital defects should prompt the clinician to check for the presence and consumption of the teratogenic plants found in the region. Investigation of toxins affecting food animal reproduction always should be done in the total context of infectious and management causes. Proper understanding of suspected toxins is necessary for correct interpretation of toxins affecting reproduction.