Production performance and milk fatty acid profile in grazing dairy cows offered ground corn or liquid molasses as the sole supplemental nonstructural carbohydrate source

Abstract

The objective of this study was to compare the effects of ground corn or liquid molasses fed as the sole supplemental nonstructural carbohydrate (NSC) source on production performance, milk fatty acid (FA) profile, grazing behavior, and N metabolism in grazing dairy cows. A strip-grazing management system was used, with cows offered a new strip of fresh herbage after each milking, resulting in approximately 16 h of access to pasture daily. Animals were fed a diet formulated to yield an 86:14 forage-to-concentrate ratio consisting [dry matter (DM) basis] of 74% mixed grass-legume herbage, 12% mixed-mostly legume baleage, 12% NSC source, and 2% mineral-vitamin premix. Twenty Jersey cows averaging (mean ± standard deviation) 121 ± 73 d in milk in the beginning of the study were randomly assigned to 1 of 2 herbage supplementation treatments: (1) baleage plus ground corn (B+GC) or (2) baleage + liquid molasses (B+LM). Both NSC sources were fed at a flat rate of 1.6 kg of DM/cow daily. The study lasted from June to September for a total of 15 wk with data and sample collection conducted in wk 3, 7, 12, and 15. Milk samples for FA analysis were collected in wk 2, 4, 6, 8, 9, 11, and 13. Data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) for a randomized complete block design with repeated measures over time. Treatment × week interactions were observed for supplement DM intake, milk urea N, bite rate, urinary excretion of uric acid, and milk FA (e.g., 17:0, 18:0, cis-9,trans-11 18:2). Supplement DM intake was greatest in cows fed B+LM in wk 7, 12, and 15. Compared with cows fed B+GC, those fed B+LM had lower concentrations of milk urea N in wk 7 and 15. Milk yield, concentrations and yields of milk components, and plasma concentrations of essential AA, except Met, which was lowest with feeding B+LM, were not affected by supplementation. The plasma concentration of urea N was lowest with feeding B+LM. Cows fed B+GC spent more time grazing than those fed B+LM. Feeding B+GC increased cis-9 18:1 FA and most trans-18:1 FA in milk, whereas B+LM increased Σ odd-chain FA, Σ n-3 FA, and the trans-11 18:1 to trans-10 18:1 ratio, and decreased the n-6 to n-3 ratio. Based on current results, B+LM can entirely replace B+GC without negatively affecting milk yield or yields and concentrations of milk fat and true protein, while decreasing milk urea N, plasma urea N, and the milk trans-11 18:1 to trans-10 18:1 ratio, and increasing Σ n-3 FA.

Replacing ground corn with incremental amounts of liquid molasses does not change milk enterolactone but decreases production in dairy cows fed flaxseed meal

“…Sucrose was the predominant sugar found in LM, accounting for 77% of the total individual sugars measured chromatographically ( sucrose and total individual sugars in LM fed in the present study were similar to those obtained by Brito et al (2017), but 38 and 49% lower, respectively, than values reported by Brito et al (2015), thereby showing substantial variation in sugars content from source to source. As expected, the concentration of WSC, which was measured colorimetrically, was greatest in LM (Table 1).…”

“…Furthermore, Σ 18C FA also decreased linearly (Table 5), indicating less uptake of preformed 18:0 from plasma by the mammary gland, possibly as a result of reduced 18:0 intake. Similarly, we observed that the milk proportion of 18:0 decreased in dairy cows fed grass hay (Brito et al, 2015) or pasture (Brito et al, 2017) supplemented with LM versus GRC. In contrast, although intake of 16:0 reduced linearly (P < 0.01; data not shown), the milk proportion of 16:0 increased linearly (Table 5), suggesting enhanced de novo synthesis of 16:0 in the mammary gland or uptake from plasma; in fact, Σ 16C also increased linearly in the present study (Table 5).…”

“…Brito et al (2015) observed no effect on milk yield when comparing GRC versus LM as the sole NSC supplemental source, but both 4% FCM and ECM yields decreased significantly in LM cows. Recently, we reported that yields of milk, 4% FCM, and ECM were not changed in grazing dairy cows fed GRC or LM as the sole NSC supplemental source (Brito et al, 2017). Collectively, these results suggest that differences in the ingredient composition of the basal diet, level of molasses fed, forage source, and forage-to-concentrate ratio, among other factors, may be responsible for the inconsistent responses on yields of milk, FCM, and ECM across the literature.…”

“…However, Baurhoo and Mustafa (2014) reported no effects on concentrations and yields of milk fat, protein, and lactose by substituting high-moisture corn with different levels of dried molasses. When GRC or LM was fed as the sole supplemental NSC, yield of milk fat decreased in dairy cows fed grass hay (Brito et al, 2015), whereas concentrations and yields of milk fat, true protein, and lactose did not change in those fed pasture (Brito et al, 2017).…”

“…There has been a continuous interest in the use of sugarcane molasses in both conventional (Broderick and Radloff, 2004;Martel et al, 2011;Siverson et al, 2014) and organic (Soder et al, 2012;Brito et al, 2015Brito et al, , 2017 dairy systems in the United States. Whereas conventional dairy cows have been fed dried molasses or LM accompanied by other NSC supplements and corn silage (Broderick and Radloff, 2004;Martel et al, 2011;Siverson et al, 2014), organically certified dairy cows are typically fed LM as the sole NSC supplemental source to grass hay (Brito et al, 2015) or mixed grass-legume pasture (Soder et al, 2012;Brito et al, 2017). Previous dose-response studies resulted in inconsistent responses on DMI, milk yield and composition, and nutrient digestibility when dried or LM partially replaced high-moisture corn (Broderick and Radloff, 2004;Baurhoo and Mustafa, 2014) or GRC (Martel et al, 2011) in moderate-to high-starch diets.…”