Strategic grazing management decreases nitrogen excretion intensity of dairy cows

Camila Delveaux Araujo Batalha,Guilhermo Francklin De Souza Congio,Sila Carneiro Da Silva,Flávio Augusto Portela Santos

doi:10.1590/1678-992x-2020-0251

Camila Delveaux Araujo Batalha, Guilhermo Francklin De Souza Congio + Show 2 more

Open Access

https://doi.org/10.1590/1678-992x-2020-0251

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Abstract

There is limited information regarding both nitrogen (N) and energy partitioning of dairy cows grazing well–managed tropical pastures. The objective of this study was to investigate the N and energy partitioning of mid–lactation dairy cows on rotationally grazed elephant grass using two pre–grazing targets: 95 % or maximum canopy light interception (LI95% or LIMax) during regrowth. The study used 26 Holstein × Jersey dairy cows arranged in a randomized complete block design with three 40–day periods of sampling. Grazing at LI95% increased organic matter and crude protein intake by 20 % (p ≤ 0.05) which resulted in a 9 % increase in fat corrected milk yield (p ≤ 0.05) relative to LIMax. Cows grazing at LI95% had greater concentration of total volatile fatty acids, butyrate and valerate (p ≤ 0.05), and smaller acetate (p ≤ 0.05) than those grazing at LIMax. Intake of net energy for lactation (NEL) and NEL secreted in milk were greater (p ≤ 0.05), while partitioning of NEL towards maintenance tended to be greater (p = 0.07) for cows grazing at LI95% than those grazing at LIMax. Milk urea nitrogen and both urine and fecal N excretion were greater for cows grazing at LI95% (p ≤ 0.05), but N excretion intensity was lower than in cows grazing at LIMax (p ≤ 0.05). Strategic grazing management using the LI95% pre–grazing target increases N losses through both urine and feces; however, it reduces N excretion intensity of dairy cows by 9 %.

Highlights

Most dairy operations in the tropics are represented by pasture–based systems (Congio et al, 2019)
The herbage crude protein (CP) content was greater for LI95% than LIMax (p ≤ 0.001; Table 1)
There was no difference between treatments during P1 (19.2 %; p > 0.05), herbage CP content was greater for LI95% than LIMax during P2 (21.3 vs. 18.4 %; p ≤ 0.05) and P3 (22.7 vs. 20.6 %; p ≤ 0.05)

Summary

Introduction

Most dairy operations in the tropics are represented by pasture–based systems (Congio et al, 2019). Several studies showed that regrowth interruption when canopy LI reaches 95 % minimizes stem elongation and senescence, generating leafy swards with greater herbage nutritive value, favoring animal performance (Voltolini et al, 2010) and contributing to the reduction of GHG gases emissions (Congio et al, 2018, 2019) These intensively managed systems are usually coupled with moderate or high doses of nitrogen (N) fertilizers resulting in high herbage crude protein (CP) content at the expense of energy content (Danes et al, 2013), which could lead to CP overfeeding of grazing dairy cows (NRC, 2001). We hypothesized that CP intake increases in dairy cows grazing at LI95%, leading to greater N excretion through urine and feces; it could be compensated by greater milk yield, allowing the reduction of N excretion intensity

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