Effect of storage time on chemical, physical and microbial composition of total mixed rations for lactating dairy cattle.
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Total mixed ration (TMR) is a method of feeding that has revolutionized the dairy sector. The purpose of TMR diet is that each cow consumes the required level of nutrients in each bite. However, aerobic spoilage during storage has been reported to greatly reduce feed quality and dairy cattle performance. The purpose of this study was, therefore, to assess the dynamic changes in chemical, microbial and physical quality of TMR that occur during air exposure to deepen the understanding of aerobic deterioration, cause of spoilage and feed quality changes overtime. Maize silage, Chloris hay, wheat bran, molasses, Maize grain, Soybean meal, rice bran, common salt, bentonite, limestone, di-calcium phosphate and mineral powder were mixed in a ratio of (307.3:53.8:110.5:27.6:35.3:71.8:110.2:0.2:4.9:29.5:21.7:1.7) to formulate a TMR ration. Without compaction, 3 kg were sampled from a TMR produced at the National Livestock Resources Research Institute (NaLiRRI) and kept in sterile polythene sample bags with the upper surface exposed to air. Samples for analysis were collected every after 6 hours for the first day and 12 hours thereafter for the subsequent two days. Samples collected at 0, 6, 12, 18, 24, 36, 48 and 72 hours were used to assess the dynamic changes in chemical, microbial and physical quality of the TMR. Aerobic stability test showed that TMR started to deteriorate at 5 h of aerobic exposure when the TMR temperature was 2℃ above ambient temperature. The pH linearly increased (p<0.0001) with increasing storage time. Dry matter (DM) and organic matter (OM) decreased at an increasing rate (p<0.0001) with storage time. Moisture content and ash increased at a decreasing rate with increasing storage time. pH and ash increases where significant at 12 and 18 h respectively while OM and DM decreases were significant at 18 and 12 h respectively. Moulds and enterobacteria linearly increased (P<0.05) with storage time while yeast, lactic acid bacteria and aerobic bacteria increased at a decreasing rate (P<0.05) with storage time. Regression analysis showed Lactic acid bacteria (LAB) to have the highest proliferation in the first 6 hours, followed by yeasts, aerobic bacteria (AB), moulds and lastly enterobacteria (EB) with simple linear regression coefficients of 0.84, 0.55, 0.33, 0.23 and -0.37, respectively. The regression coefficients of LAB, yeasts, moulds and aerobic bacteria showed a sharp increase (p<0.05) at 12 hours while enterobacteria showed a sharp increase (p<0.05) at 36 hours. TMR, when exposed to air deteriorates rapidly, due to changes in physical, chemical and microbial composition thus high losses of nutritional components. Yeasts and aerobic bacteria were responsible for initiation of aerobic deterioration. Enterobacteria and moulds tended to play a secondary role in TMR deterioration. Deterioration occurred within 5 hours of aerobic exposure. Therefore, yeast and aerobic bacteria are the major player in initiating aerobic spoilage in TMR.